Fresh Water Systems
Fresh-water diving is often overlook in parts of the world where the sea is readily accessible. However diving in fresh water can be a very worthwhile experience, especially if you take care to locate good dive sites.
Rivers, especially short fast-flowing rivers with rocky beds can have deep pools with excellent visibility. This is dependant on reduced sediment levels and is best during early summer when there tends to be reduced water flow. River depth in Britain rarely exceed 2-3 meters in depth except in pools and gorges. The deepest British river pools are about 15 meters in depth.
For most divers fresh-water diving is synonymous with lake diving. Lakes can vary from small ponds to major inland seas. In britain, the lakes and lochs are quite small, although they have some intriguing features. Below 6 meters, most British lakes consist of featureless, silty bottoms, although occasionally there are underwater cliffs and silt-covered rocky slopes. Lake depths in Britain are usually between 15 and 75 meters, although in Scotland they are much deeper, with the deepest being Loch Morar at 310 meters.
Flooding gravel pits and reservoirs are very useful for training. Canals can be very choked with debris but can often be the home of interesting small forms of life. Cave diving is usually undertaken in fresh-water but is a very specialised technique requiring special training.
Locating good fresh water sites takes some care. There are very few lakes or rivers for which charts are published. Clues from ordinance survey maps may indicate areas where gorges or pools might have formed, also steep contour lines running across to a lake often mean the lake itself will have a steep, rocky slope. Sometimes useful information can be found in publications intended for fishermen or canoeists.
The geological formations found in fresh-water diving can be one of the main attractions for divers. River chasms are fascinating places to explore with a scuba equipment. Be very careful not to be swept under underwater overhangs or into gorges or other places from which you cannot escape.
Many rivers flow through a series of deep pools and in Britain these can occasionally reach 15 meters or so in depth. Often the home of many fish these dive sites can offer excellent diving.
Pools and gorges are often formed in places that are geologically interesting. The water may have cut the riverbed along the line of a geological weakness or, sometimes, may have cut across a dyke of intrusive rock. Such features are usually very rewarding to explore.
Waterfalls occur on many rivers and often have a deep pool at their base. It is possible to swim right under the waterfall if the flow isn't too intensive. It must be said that some rivers waterfalls and pools are inhospitable and can be downright dangerous to dive in. Afterall you wouldn't want to literally 'dive' off the waterfall, would you?
Most of the features discussed above are best found in rivers. However, lakes can also provide unusual geology in the form of steep or even vertical rock walls. These are usually found in lakes or lochs that have been formed by the flooding of glacial valleys long ago, the ice having previously cut steep sidewalls. In the UK there are walls that run vertically to depths of at least 80 meters in some Scottish lochs. Even for experienced divers these dive sites can prove to be quite challenging.
Aquatic Life in Fresh Water
Fish life can be one of the factors that make fresh-water diving worthwhile. Salmon can often be seen in rivers and there are few experiences to compare with diving in the center of a large salmon pool. Trout are often seen, although they aren't quite as superior as salmon. Eels can be very common in rivers in summertime and they can range from very small to as thick as a mans arm, the latter being disconcerning in low visibility. Rivers may also contain the colourful perch, whereas the predatory pike is more a fish of the lakes. The large pike is a formidable fish, but there is no record of one attacking a diver.
Fresh water contains lots of other life. Fresh water crayfish are not often seen, although they are not uncommon in British rivers, frogs, toads and newt can be seen in small expanses of fresh water.
It is worth bearing in mind that some bodies of fresh water can be polluted with corrosive industrial chemicals or with disease-bearing organisms. Common sense will be a good guide to not diving in such places. Local diving clubs can often advise on where the danger areas are for fresh water diving.
The Law and Access
Most areas where there are lakes and rivers are owned by someone or at least the access to the water itself. It is wise to check if there are any restrictions on diving. It can be unfortunate but dive site owners in the UK can, shall we say, be somewhat 'Enterprising' and insist on charging divers for the use of the water or access to the dive site. While this can vary, some charges can be excessive given the number of divers using the area!
On some rivers and lakes the right to fish is jealously guarded, as a result divers may not be permitted to dive in them. It is therefore wise to check you are allowed to dive there first. Again, local dive clubs and centers are good places to check on this.
Fresh Water Diving Overview | Fresh Water Diving Techniques