Freshwater Snorkeling/Diving

[ScienceSteve]

I am a watershed ecologist and I would like to start making videos of the sub-surface worlds we drive by everyday. I've spent a bit of time snorkeling off the SoCal coast, and I have a little bit of experience snorkeling in lakes, but none in streams or rivers. The reason I don't have much more experience is that I am not familiar with the dangers of swimming sub-surface in fresh water. The rivers and lakes I work are heavily fished, so I know about the fishing tackle hazard, and I'm below the altered tables elevations, but what other hazards should I expect to encounter? Also, if you have ever become tangled in line, what was it like? And, oh yeah, I'm signed up to go for my PADI cert after summer semester ends.

 

[TMHeimer]

I've done very little in fresh water, but there is the obvious. Most parts of most lakes have no current, but there can be some if the lake is part of a river system. Obviously know the speed of a river current (and where it may be greater). Usually less current closer to shore. Know the bottom topography--what can you bump into or get caught in when in current. If the rivermouth enters salt water there is of course the tides--and halocline, which can be a little disorienting. The Hudson River flows upstream (brackish) at least 30 miles N. of NYC--maybe much more. Oh, don't dive the Hudson River unless searching for Jimmy Hoffa.

 

[Subcooled]

The (fast) current may pin you against a submerged obstacle (fallen trees, metal grilles, ...)
Avoid small cracks that only let the water to pass.

Carry a small cutter on your arm to free yourself from fishing nets and line, and do learn the reverse kick.

 

[Frosty]

We do drift dives down certain rivers here in NZ.Any river with a reasonable current can have hidden dangers for swimmers/snorklers.
Undertows IMO would be the major issue. -With scuba you have the time to get yourself out of trouble