Diving the Cape Peninsula and False Bay/Blue Rock Quarry
The dive site Blue Rock Quarry is a disused quarry. It is the only significant fresh water dive site with public access in the greater metropolitan area of Cape Town in the Western Cape province of South Africa.
The site is diveable in all weather conditions, and provides a large range of depths, and is useful for training and familiarization with equipment and procedures.
Near the foot of Sir Lowry's Pass, just off the N2 highway.
This site is NOT in a Marine Protected Area
The "Blue Rock Quarry" was named for the building aggregate which was quarried there in the past, which was a dark blue-grey colour. The quarry was closed and is now flooded and used for water sports including diving.
The bottom is stepped, except at the old access roads. The level at the west end and the west part of the south and north sides is at about 10m, then drops almost vertically to about 20m, then further east it drops off again more gradually over a boulder slope to the main level at about 25 to 30m. The East end is deeper, from 30 to 40m in most places, and the deep area in the south east corner extends to at least 47m, though there are unconfirmed reports of greater depth.
Visibility varies with the seasons. It is best at the end of summer, before the winter rains, which reduce visibilty due to runoff. Visibility can be as high as 6 to 8m but is usually more like 3 to 4m, and the bottom is covered with fine silt which can reduce visibility to less than a metre locally in seconds. The silt usually clears overnight to the usual 3 to 4m. At the end of winter the water level may be as much as a metre higher, and visibility may be significantly worse, possibly 2m in the shallows and less in deeper water, and the light level will also be lower. It may be very dark below 15m, with visibility of undisturbed water about 1m.
The sides of the quarry are almost sheer rocky walls, with loose boulders and occasional slight overhangs. Care must be taken not to dislodge rocks when divers may be below. The bottom is very silty and visibility is badly affected if it is disturbed. An old access road at far side (north west corner) winds down the side of the quarry below the water.
The east end is deepest and exceeds 40m in places. Maximum depth is claimed to be over 60m in a very small area. The west end is shallower and stepped down to a flattish silty bottom at about 25m. There are large and small boulders scattered on the bottom and everything is covered by fine silt. There are submerged trees in places, mostly along the sides where the slope is not too steep, like on the old access roads. These could cause entanglement of divers equipment and due care should be taken to avoid this. There is some debris left from the quarry operators, and from the builders of the ski-tow system, and some dive schools have permanent training aids on the bottom. These should not be moved or vandalised. Two permanent shotlines are sited in the south east corner and are property of a commercial diving school.
Geology: The quarry was a commercial source of Cape Blue Rock, a dense Hornfels, (fine textured contact altered argillaceous [from clay] rocks) from the Pre-Cambrian Malmesbury series. The Hornfels was formed when the nearby Stellenbosch granite pluton intruded more than 530 million years ago.
The site is protected from most weather conditions. It can be safely dived in the strongest winds likely to occur in the area, and there is never any current or surge. The site is usually at it's best at the end of summer, when the shallower water has warmed a little and the silt from winter rain runoff has settled as much as possible, but this is an all year dive site, and conditions change very little. Visibility is usually about 3 to 5m until you disturb the sediment, when it can drop to zero in seconds.
This is an area which sometimes has a noticeable thermocline, and the depth can vary with the seasons, being deepest at the end of summer, when it may be between 8 and 15m.
Water temperature at the end of winter is likely to be around 16°C. This will be the approximate temperature below the thermocline for the summer.
Parking is adequate, and security probably not bad. Toilets and changing rooms are available, and a fast-food restourant may be open. Overhead ski-tow facilities are the main feature at this site, and may present a hazard to divers. However, as this is the main attraction, complaints will probably be a waste of breath. Keep clear of the ski zone and you will be OK, or dive on a Monday, when the ski-tow is closed.
[[|thumb|Entry area at the south east end is at the end of the access road, and is just visible at the left of the photo]] Take the turnoff to the north to Sir Lowry’s Pass village from the N2 at the Gordon's Bay turnoff at the foot of Sir Lowry’s Pass. A few hundred metres along there is a turnoff to the left to a short access road which runs more or less parallel to the main road. Turn into the gate to the left and pass through the security gate. The gatekeeper will require payment of the entry fee. Drive along the tar road and further along the dirt road until you reach the parking area near the buildings. An entrance fee of R30 and a charge of R80.00 for diving is levied per person for the day (Sept 2009). Parking is usually adequate but equipment will have to be carried about 50m to the water. Adequate paths and stairs are provided near the buildings, and old access roads provide safe access to the water at two other places. Enquire at the shop about vehicle access to these roads. Four wheel drive, differential lock and reasonably high ground clearance recommended.
There are three areas usually used for diving access.
There are small fish, freshwater crabs, Platannas (African clawed toad) and some larger fish which have not been identified, but may be carp. Small fresh-water jellyfish have been seen at some times of the year, but have not been reported recently.
Not recommended for photograpc enthusiasts as there is little to photograph, and the visibility is usually poor and the water dark.
Poor visibility in the rainy season, or when the silt is disturbed by divers. Nitrogen narcosis in deep areas, Loose rocks on walls, Submerged trees and possibly other debris. Water skiers and their safety boat under the towline.
Very suitable for training. No special skills required. The West end is relatively shallow and there are few submerged trees. For shallow water training exercises the submerged access road in the north west corner is suitable.
Not suitable for night dives as the gates close at about 17h00. A good site for deep and decompression diving training.
No special recommendations for shallower dives, except to adjust your weights for fresh water. If doing deep dives, the gas may be chosen to suit the planned profile, and a light, reel and dsmb are recommended.