Diving in Blue Rock Quarry

The dive site Blue Rock Quarry is a flooded 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.

Understand

Chart of the Blue Rock Quarry showing 10 m and 20 m contours and a few spot depths. The red line indicates the overhead ski tow cable.

The quarry is used for commercial diver training as well as recreational diving

See also: Diving the Cape Peninsula and False Bay#Understand

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. The water supply is mainly groundwater, and is neither particularly clean nor known to be contaminated with anything nasty. Water level may vary a bit, and can be a metre or so higher after a rainy winter, but is limited by overflowing at the west end. Runoff from winter rains carries in silt and reduces visibility.

Position

• S34°07.566’ E18°54.045’ 1 West end
• S34°07.646’ E18°54.220’ 2 Deep end
• S34°07.630’ E18°54.128’ 3 Floating jetty
• S34°07.540’ E18°54.137’ 4 Dive and Adventure corner

Near the foot of Sir Lowry's Pass, just off the N2 highway.

Altitude is somewhere between the 60 m and 80 m contours. Sea level equivalent altitude for most dive tables.

This site is not in a Marine Protected Area

Name

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.

Depth

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 10 m, then drops almost vertically to about 20 m, then further east it drops off again more gradually over a boulder slope to the main level at about 25 to 30 m.

The east end is deeper, from 30 to 40 m in most places, and the deep area in the south east corner extends to at least 47 m, though there are unconfirmed reports of greater depth. (65 m in the south eastern corner)

Visibility

Visibility varies with the seasons. It is best at the end of summer, before the winter rains, which reduce visibility due to runoff. Visibility can be as high as 6 to 8 m but is usually more like 3 to 4 m, 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 4 m.

At the end of winter the water level may be as much as a metre higher, and visibility may be significantly worse, possibly 2 m in the shallows and less in deeper water, and the light level will also be lower. It may be very dark below 15 m, with visibility of undisturbed water about 1 m.

Blue Rock Quarry before final filling. (photo CDS&M)

Typical rocky slope in a shallow part of the quarry

Topography

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.

View from the south east corner. The deep end is to the right of the photo. The old access road in the north west corner can be seen to the left.

The east end is deepest and exceeds 40 m in places. Maximum depth is claimed to be over 60 m in a very small area.

The west end is shallower and stepped down to a flattish silty bottom at about 25 m. 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.

There are a number of steel wire cables mooring the floating ski course accessories, rope mooring line for the ski lane demarcation buoys and there may be guide line laid by technical divers across the bottom, mostly in the deeper areas. Take care not to get snagged on any of these. Carry a suitable cutting tool in case of accidental snagging on the guide line, which is usually 1 to 2 mm white nylon braid.

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.

Conditions

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 its 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 15 m.

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.

Facilities

The restaurant and offices are in these buildings, seen here from the main parking area.

Parking is adequate, and security probably not bad. Toilets and changing rooms are available, and a fast-food restaurant 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.

Get in

The west end entry area is at the beach to the right 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 and a charge for diving of R130 is levied per person for the day (August 2016). Parking is usually adequate but equipment will have to be carried 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. Inquire at the shop about vehicle access to these roads. Four wheel drive, differential lock and reasonably high ground clearance recommended.

Opening hours vary, and the site may be officially closed between mid May and mid September. It is often possible to get access by arrangement on closed days, as some of the staff appear to live on site.

There are three areas usually used for diving access.

1. The platform where the water-skiers launch, at the bottom of a set of stairs in front of the buildings. There is an adequate set of steps at the east end of the jetty for getting out.

1. The shore at the west end, where there is easy access at the base of the north western pylon. This area may be used by commercial diver training schools, usually for scuba, but occasionally for surface supplied diving. Stay clear of their operations while they have divers in the water, or at least request permission from the supervisor, who may require you to stay clear of a specified area.

1. The shore at the middle of the south side, at the bottom of a grassed over access ramp, where there is a wood decked floating jetty used as a dock for the boat which picks up skiers who let go of the towline far from the launch area.

1. The old access road at the south east corner. There is a small concrete platform and a small roofed area which provides a bit of shade. Commercial diving schools occasionally rent this area for surface supplied training operations. If a commercial diving school has a diving operation under way the supervisor will not generally allow recreational diving on the site under his control. Do not push your luck, the supervisor is legally empowered, by the Occupational Health and Safety Act and the Diving Regulations, to have any person who in his opinion may interfere with or compromise the safety of the diving operation removed from the site. His opinion, not yours.

The commercial schools do not usually work on weekends. If there is commercial training going on, just use one of the other access areas.

See

View of the Blue Rock Quarry looking west from the road near the access gate.

Shoal of small fish

Aquatic life

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.

Features

There are several water-ski ramps with cable moorings, but stay away from these when the ski-cable system is in use. The east end has a few permanent shotlines used by the commercial diving schools and by free-divers for training. If they are not in use there is no problem with using them. The submerged roads at the west end have an assortment of earthmoving vehicle tyres lying around where they were last left by trainee divers who use them for lift bag exercises, and there is some steel structural framework at the ski launch platform at the bottom of the stairs in the south-west corner.

Photography

Not recommended for photograph enthusiasts as there is little to photograph, and the visibility is usually poor and the water dark.

Routes

1. Multi level dives are easily made near where the road enters the water. The road can be followed, or by swimming at right angles to the road, the depth increases in steps to about 25m at the west end. Take care to keep clear of the water ski route under the cable system when near the surface.
2. Deep dives can be done using the moorings of the rafts as shotlines, or for greater depth shotlines can be set up to suit the dive plan. If it is expected to obstruct the ski zone, be sure to make arrangements with the management ahead of time. There are two permanent shotlines belonging to the commercial diving school, which may be used if they are not operating on site.
3. If there are no commercial diver training operations in progress, the permanent shotlines may be used. The further from the entry area at the base of the south-eastern access road is anchored at about 42m on a rubble bottom. The slope up appears to be nearby, about 2 m away, but it is not known in which direction, or of this will provide a direct ascent, or an ascent to a higher level ledge, which is most likely.
4. The nearer shotline is anchored on a submerged access road at 27 m. There is usually a diver training aid for underwater assembly exercises there. Swim north east across the road to the dropoff which slopes down at about 45 degrees. This probably goes down to about 42 m. You can return up the rockface, or if you have used a reel, back to and up the shotline. The rockface above the road is nearly vertical, and has some loose fragments, so keep your group at the same depth, spread out a bit and stay a metre or so off the wall for safety. Do not have more than one group on the wall at diffiernt depths, as the risk for deeper divers of being hit by a falling rock is unacceptable.

Stay safe

Preparing a surface supplied helmet diver for the water

See also: Diving the Cape Peninsula and False Bay#Stay safe

Hazards

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.

Skills

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.

Equipment

See also: Diving the Cape Peninsula and False Bay#Equipment

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.

Back to Diving the Cape Peninsula and False Bay#Fresh water dive sites