Diving the Cape Peninsula and False Bay/Steenbras Ridge

The dive site Steenbras Ridge is an extensive offshore rocky reef in the eastern central area of False Bay, near Cape Town in the Western Cape province of South Africa. There are several named dive sites and landmarks on this reef, which has not yet been fully explored, though it has been mapped by metre resolution multibeam sonar, mostly by the South African Council for Geoscience, and partly by Wreckless Marine.

This region is a long ridge running approximately north/south, about two thirds of the way across False Bay. Some of the sites not dived very frequently as it is a long boat trip and visibility is not very predictable, though it can be better than other sites on the east side of the bay. Depth varies considerably, with the northern sites relatively shallow, and the southern sites pushing the limits for recreational diving on air and nitrox.

This site is not in a Marine Protected Area (2004). A permit is not required.

The name "Steenbras Ridge" refers to the geomorphology of the area and the geographical proximity to the Steenbras River, the largest river entering False Bay on the east side. The largest and longest known shoal areas on the ridge are the dive sites at Steenbras Deep Reef North and South Pinnacles, which have been known as dive sites since the 1980s and by fishermen for longer. The name has simply been extended to the rest of the reef. The river may have been named for any one of the fish species termed "Steenbras".

Maximum depth tends to be greater for the sites which are further south, and minimum depth depends on local topography. As sites tend to be selected for exploration when the relief is high enough to show up on sonar equipment, the named sites tend to have shallower points than the unnamed areas nearby. However, the local depth variation is not usually large compared to other sites in this region, and is usually less than about 10 m over quite large areas. This does not mean the area is flat, as the local depth can easily vary by two to five metres over a short distance.

Visibility is not easy to predict, but can be better than other east False Bay sites if there is a red tide, as it is deep enough that the bottom water may be clear, though the light level may be low. It can be better than 10 m on the reef while the surface and top several metres has less than 3 m viz. Good visibility at the surface may not predict good visibility near the bottom. There have been occasions where a band of poor visibility occurs in mid-water with better visibility both above and below. This does not appear to be explained in the scientific literature, but may be associated with a thermocline. The sites further south are generally likely to have better visibility on a given day as they are further from the eddy which may form off Gordon's Bay, and which can retain murky water.

The sites are all on hard sedimentary rock with significant dip. The ridge appears to be the remains of the other side of the fold which forms the Hottentots Holland mountain range, but there is no data available for exactly which strata, and they could be strata exposed in the mountains to the east, or strata underlying or overlaying these. As a consequence, there is a sense of continuity between the sites, though there are also clear differences in how the various layers have weathered. It is also apparent that the erosion and weathering of the bedrock mostly occurred when the rocks were above sea level, and exposed to atmospheric conditions, though there are adjacent areas of smaller boulders and cobbles which show characteristics of wave or fluvial rounding.

The site is exposed to wind and waves from all directions, however it is quite deep, so short period waves will not affect conditions on the bottom greatly. Low short swell, light wind is best. There may be a thermocline, and the visibility may change significantly below the thermocline. 17°C at the surface with 2 to 5 m visibility above the thermocline and 11°C with 8 to 10 m visibility below the thermocline is possible and conditions at depth are not easily predictable. There is no specific time of year for diving this site, you just have to wait for low swell and light winds.

A light current has been reported occasionally, particularly at the surface, which can make it tricky to find the right part of the reef without a heavy shotline. This current has been measured at 0.9 km/hr setting SSE, but other directions and strengths are possible. The surface current is usually wind driven, and will therefore flow left of the wind direction due to Coriolis effects, but will lag a bit when the wind changes.

The sites are only accessible by boat, usually from Gordon's Bay Old Harbour or Harbour Island marina.

Anchoring is not recommended. Most of the sites are on unpredictable holding ground, and there is a good chance that the anchor will either drag or foul, possibly both, and a rope rode may chafe through during a dive. This is a site where only the suicidally foolhardy would dive from an unattended boat, as it may not be possible to swim back to the boat on the surface due to current, and besides dragging or fouling, the anchor tackle will do undesirable and unnecessary ecological damage. Leave the boat in the charge of a competent person who will be able to pick up stray divers and call for help in an emergency. If for some reason you really must dive from an anchored boat, a distance line to either the anchor cable or directly to the boat will improve the chances of getting back safely.

Dive at some of the known drop points listed here, and explore the local reef around each point. Alternatively, dive at an undescribed place and let us know what you find.

• -34.13341718.75451 Choirboys Reef: S34°08.005' E18°45.270'.

  

  

  This site is far enough offshore to be generally outside the eddy of low visibility that often occurs off Gordon's Bay, but is still reasonably close to the launch sites, and has good biodiversity and more rugged topography than most of the close offshore sites of the area. It appears to be a fairly small area and is mostly unexplored. The area is indicated on the SAN chart as a small shoal area above 20 m, with a spot depth of 18 m. The reef is named for the colonial ascidian "white choirboys", which is quite common at this site. Maximum depth at the site is about 26 m. and the top of the reef is about 21 m. (Average depth of a dive is likely to be about 23 m which is too deep for entry level divers). Visibility is likely to be better than at the Gordon's Bay inshore dives, as it is outside the Gordon's Bay eddy, but is unpredictable. Surface conditions may not accurately predict bottom conditions, particularly in late summer and autumn, after the thermocline develops. The site is a slightly raised area on the ridge which runs out from off Strand to Steenbras Deep. There is not a lot of variation in depth over the site, and reef profile found has mostly been 2 m or less. The surrounding reef is very flat. The ridges tend to run roughly north-south, following the strike of the strata, probably Pre-Cambrian sedimentary rock of the Tygerberg series. Strike is probably roughly north-south, Dip appears to be steep. The site is about 10 km from Harbour Island, or (distance)km from Gordon's Bay old harbour.

• -34.14268318.7638172 Drop Zone:S34°08.561' E18°45.829'. About 8.6 km west (276°true) of Harbour Island. The name "Drop Zone" was given to the site by Indigo Divers of Gordons Bay. Maximum depth is about 26 m, and the top of the reef is about 12 m according to the official SAN charts. Average depth of a dive is likely to be about 18 m. Moderate and low profile high rugosity rocky reef. The very steep dip results in many ridges and gullies, mostly not very deep. There are few landmarks of note. The reef is hard, resistant, sedimentary rock, possibly of the Precambrian Tygerberg formation. Strike appears to be northwest-southeast, with nearly vertical dip. The site is about 8.6 km from Harbour Island slipway, or 9.2 km from Gordon's Bay Old Harbour. Marine life includes large numbers of gorgonian sea fans, shoals of juvenile fish, and the usual variety of echinoderms, sponges and anemones. Not much seaweed, which suggests that the reef is not exposed to much light, which means that the visibility is not often very good. In 2014, it was free of the massive brittlestar populations common on the Cape Peninsula sites. This site has a comfortable range of depths for recreational diving, and is reasonably close to the slipways at Gordon's Bay, while being far enough offshore to have a fair chance of better visibility when visibility is poor at the shoreline sites of eastern False Bay. Biodiversity is fairly high and the site is large.

• -34.15606718.750653 Sterretjies Reef: S34°09.364' E18°45.039' (Usual drop point).

  

  The area is indicated on the SAN chart as a shoal area above 20 m, with a spot depth of 15 m. The name "Sterretjies Reef" refers to the large number of juvenile basket stars seen there. Sterretjies means little stars in Afrikaans. The site was named by Indigo Divers when they first dived there in 2018. Access is by boat, usually from Gordon's Bay or Harbour Island. The site is about 10 km from Harbour Island, or (distance)km from Gordon's Bay old harbour. The site is borderline for entry-level certification, as most of the reef is below 18 m depth, and good buoyancy skills are required to avoid damaging the fragile reef life. Indigo Divers report that there were lots of fish, large sea fans and sponges. The pinnacles are covered with soft corals, sponges, multi-coloured sea fans and strawberry anemones. Various colour morphs of gas-flame nudibranch, frilly nudibranchs, orange-eyed nudibranchs, crowned nudibranchs, white edged nudibranchs, soft coral nudibranchs and candy nudibranchs. Fish included white seacatfish, blennies and shy sharks. Other invertebrates included walking anemones, spider crabs, sea spiders and octopus.

• -34.17681718.7748834 Steenbras Ridge Edge: S34°10.069', E018°46.493'. A long straight north/south step between reef to the west and a large expanse of sandy bottom to the east. Flat sand at about 32 m with small wave ripples east of low sandstone? reef sloping gradually upwards to the west at to the south of the step.

• -34.18796718.7633335 Steenbras Ridge Outpost: S34°11.270' E018°45.804'. A small outlier to the east of the ridge, comprising a small area of jagged edged outcrop with steep dip, rising a few metres above a larger are of low reef of rubble, mostly in the sub-metre size range. Ecology typical of reef in this area and depth.

• -34.18833318.7591336 Steenbras Ridge River Mouth Pinnacle: S34°11.300' E018°45.548'. Small low pinnacle with high dip of about 80°, strike roughly north/south. The rock is eroded to sharp edges on top, much like some of the dark fine-grained Tygerberg stuff and very much like the pinnacles at Steenbras Koppie a few kilometres further south.

The name "Steenbras Deep" is a contraction of "Steenbras Deep Reef". This has been the name used by divers and fishermen for this reef for decades at least, and is more likely to refer to the nearby Steenbras River than to any of the fish species known as Steenbras, though this is also a possible derivation.

Geology: The geology of the area is not known, but the rock is sedimentary, and the shape of the reef is more consistent with sandstone than shale, as it has a chunky, squared off looking structure, much like the Rooi-Els reefs. Strike is not recorded, but dip may be steep, based on the shape of the ridges and gullies. The rock is very similar to that of Drop Zone and Sterretjies. The north-westerm section of the South Pinnacle area appears to have near vertical dip, and the top surface of the outcrop is quite jagged, similar to outcrops of dark rock at Blousteen and Gordon's Bay, which are known to be Tygerberg formation. The surrounding bottom in this area includes large areas of water-smoothed shingle.

• -34.202518.75957 Steenbras Deep North Pinnacle or 2nd Pinnacle: S34°12.148' E018°45.568'. About 6 km west of Boskloof Point and Steenbras River mouth, and shown on the SA Navy charts but not named. Irregular shaped reef about 40 m diameter at 21 m, of hard, fine-grained sedimentary rock. Some jointing or bedding planes about N-S magnetic. If this is the strike then dip is very steep, nearly vertical. A sample of rock has been collected and awaits analysis. The pinnacle is irregular in shape, with a large number of cracks, grooves and indentations, mostly not very deep. Sand is coarse and shelly with lots of bryozoan detritus at the edge of the reef at about 29 m. The top of the pinnacle is at about 18 m. There is a small section of lower reef to the south-west, mostly deeper than 21 m. North Pinnacle (2nd Pinnacle) is about 18 m at top and about 27 m at the sand. The site is only accessible by boat. It is approximately 10.5 km from Harbour Island, or 10.1 km from Gordon’s Bay harbour.

• -34.210718.75838 Steenbras Deep South Pinnacle or 1st Pinnacle: S34°12.640' E018°45.500'. About 6 km west of Boskloof Point and Steenbras River mouth, and shown on the SA Navy charts but not named. Large area of irregular shape, about 130 m east to west and 200 m north to south at 27 m, with the top at about 18 m. Perimeter drops off fairly steeply, with several large and fairly deep gullies cutting into the outcrop from several directions. There are sand patches at about 30 m depth scattered around the outcrop, and more reef in other places. There are also a few 18 m pinnacles near to the plateau area. There are places with a fairly flat shingle bottom adjacent to the reef. South Pinnacle (1st Pinnacle) is about 17 m at the highest point, and 30 m maximum depth. The site is only accessible by boat. It is approximately 10.5 km from Harbour Island, or 10.1 km from Gordon’s Bay harbour.

• -34.21721718.7625839 Snake Ridge: S34°13.033 E018°45.755' Sedimentary rock outcrop, south of Steenbras Deep, which has a sinuous ridge top running approximately north/south, giving a snake like appearance on the map, guessed to be Peninsula sandstone or similar blocky rock. Relatively low profile except for the ridge. Strike somewhere near N/S, dip may be steep? Ridge meandering and discontinuous. Snaky description from appearance of the sonar bathymetry image, which is Probably 1 or 2 m resolution.

• -34.2241518.76156710 Steenbras Koppie: S34°13.449' E018°45.694'. Small close cluster of steep sided high profile outcrops with shelly sand between. Rock looks like it may be Tygrberg shale, with ragged tips and edges, strike roughly north/south, dip steep, maybe 60° or more.

There is quite a good variety of invertebrate life on the reef. It is similar to, but has a slightly different ambience compared with the reefs on the east shoreline, and is very different to the granite reefs on the west side of the bay. Much of the reef has high profile, and the surface is generally rugose, with a lot of decimetre scale complexity, including quite a number of narrow crevices which can trap a shot-weight. There is a high density of soft coral and sponge cover which is spectacularly colourful when the coral polyps are open.

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  Olive soft coral at Drop Zone
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  Striped anemone Anthothoe chilensis at Drop Zone
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  Highfin klipfish on Palmate sea fan at Drop Zone
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  Basket star Astrocladus euryale at Drop Zone
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  Papery burnupena on lacy false coral at Drop Zone
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  Multicolour sea fan at Drop Zone
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  Red chested and Mauve sea cucumbers at Drop Zone
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  Black nudibranch at Drop Zone
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  Golden sea cucumbers at Drop Zone
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  Scrolled false corals at Drop Zone
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  Elegant feather stars at Steenbras Ridge River Mouth Pinnacle
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  Tubeworms at Steenbras Reef Edga
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  Reef invertebrates at Steenbras Reef Edge
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  Invertebrate reef cover at Steenbras Koppie
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  Sponge at Steenbras Reef Outpost
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  Seacatfish and sponges at Steenbras Reef Outpost
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  Crab on sea fan at Steenbras Reef Outpost

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  The Frilled nudibranch, Leminda millecra is fairly common at Steenbras Deep
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  The reef at Steenbras Deep
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  Violet spotted anemone and soft corals at Staanbras Deep
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  Sponge at Steenbras Deep
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  Sponge at Steenbras Deep

The sites are generally good for macro photography. The visibility is unpredictable, and often not very good, so lenses suitable for close-up work are most likely to produce good results, and artificial lighting will be necessary in almost all circumstances. External flash is recommended to minimize backscatter.

No particular routes recommended.

Strong winds may develop over a short time, however these are usually predictable, so check the weather forecast. There is often a slight current, so do not leave the boat unattended. For preference ascend on the anchor line or a shotline, otherwise a SMB should be used. These are not good places to be lost.

The ability to deploy a DSBM is recommended. Some of the sites are not suitable for novices as the depths may be beyond their extreme limit and the sites are far offshore.

A light can be useful if the visibility at the surface is bad. A reel and DSMB are highly recommended, so the boat can find you if you drift away, Nitrox can greatly extend no-decompression time. A dry suit would be good if diving on Nitrox, as it may be quite cold at the bottom.

Other offshore dive sites of eastern False Bay:

• -34.14833318.6463891 East Shoal
• -34.152518.82752 Moddergat
• -34.22798318.6381673 SATS General Botha
• -34.244318.66594 SAS Bloemfontein

Back to the Alphabetical list of sites, or list of reef dive sites in the northern False Bay offshore area

Other regional dive sites:

• Dive sites of Table Bay and approaches,
• Dive sites of the Cape Peninsula west coast
• Dive sites of the Cape Peninsula east coast
• Dive sites of False Bay east coast
• Fresh water dive sites of the Cape Town Metropolitan Area