Alternative Names: Dorothea
Type of Dive: Fresh water quarry
Travel directions: Take the A487 to Porthmadog. About 2 miles out of Caernarfon turn left at a roundabout and follow the road into Penygoes. Turn left onto the B4418 and follow the road into Nantle, shortly before Nantle you will see a large lake on your right, just past the lake on the left is a row of houses, turn left along these and follow the track to the quarry. On the way along the track you will pass the posts of the former gate. Be warned that the track up to the quarry is pot holed and will test you vehicles suspension.
Parking directions: There is a car park at the top of the site but the ramp to the entry slab is very steep, a serious consideration if you're carrying a lot of kit, and the site can get quite crowded at weekends.
Lat & Long: 53° 1' 39.41'' -4° 8' 44.39'' Google map
Depth: Dorothea has a max of 104.5m deep, in the sump tunnel, but most of it bottoms out at around 87 ish, you can get a little deeper in the two small sumps, but only a couple of metres really.
Site entry/exit: When you enter the water you can stand up, then descend down a slope to a small 3m shelf, descend down another shelf to 6m, another slope to 9m
Underwater directions: If you swim to the right following the 9m shelf round you come to a wider area where the crane is. You can drop off here and descend to a shelf at 22m where you have a couple of options. From here you can either swim to the left where this shelf widens out, and head towards the first set of pinnacles which have a tunnel through them and some slate huts around their base and either follow the slope down to 40m and the gnome garden, or swim up the slope and back to the exit platform (It's worth noting here that there are two steel cables running up the side of the pinnacle which you can use to ascend to the surface if you don't want to swim back up the slopes) There is also a small sump to the left of the pinnacles which bottoms out at about 35m.
If you turn right at the 22m shelf you can drop first to a 40m ledge or continue down into one of the two bottom sumps (about 85m) If you follow the quarry wall around in this direction you can do deeper dives around the bigger pinnacles or take a look at the car stack (People have been dumping cars in here from the same point for years, so the car stack starts at about 85m with the latest additions on top at a depth of about 40m.
There are two gnome gardens in about 40m, the most dived of the two has a buoyed rope tied off to it, and from this shelf you can drop over the edge to a long tunnel at 56m, or drop even further into the bottom where there is another tunnel at 90m and beyond that the sump, with a hut and a small blast tunnel, which is closed at the far end. This is the deepest point. Summer temperatures in the shallows can reach 16 degrees, as you descend to 25m it drops to about 9 in the summer and seven in the winter, as you drop to 40m it's a uniform 7 and drop to the bottom it's about 4 degrees. Diving to the bottom is better done in summer, when you can at least warm up in the shallows on deco.
Air & Nitrox fills: Air fills can be obtained from Vivian dive centre in Llanberis, but there are no facilities for nitrox or trimix, so if you're here for a weekend you'll need to bring your own.
Site Hazards: Temperature and depth.
Nearest Public phone: The local village
Mobile Network service: There are no on site facilities, no toilets, no phones (and mobile phone reception can be variable) and no food outlets,
Café: Although there are shops, cafe's and pubs in the local village, these are not within walking distance, so you need to take hot flasks, brewing kit, butties etc
Created by: Leigh
Thanks To: Lizardland for the pictures
Other comments: Dorothea's reputation as a dangerous quarry is undeserved. You have to swim out quite a way before you come to any drop-offs, until you get to 40m, the depth progressions are down slopes, so the bottom is always visible. Obviously, because of it's extreme depths, a diver who goes looking for trouble is going to find it. The vis is usually very clear, although there is sometimes a seasonal algae bloom which can drop the vis, certainly in the shallows, dramatically, to as little as 2 or 3m, but this is usually short lived. It is, however usually dark, except in the shallows on very sunny days, so divers need a torch.
Underwater photos: To Follow
Divesite map: By Richard Bufton below NWSAC Map