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salt water vs. fresh water

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New Member
Sep 12, 2003
I'm going to be doing some training dives in fresh water. Should I plan on diving shallower than in salt water, and if so how much shallower (in terms of percentages)?

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Reactions: Pezman
Hi Michael
Long time a go I send a formula that I use to calculate equivalence between performances in lake and sea take a look at:

The main differences are:
Cold= Usually lakes are colder than sea, but not in all places, so you must take into account wetsuit width (or no wetsuit)
Density= As you know fresh water has less density than salt water, so you will find that it's easier the descend phase of the dive, and you will feel less propulsion on the ascend, so you have to balance your ballast
Altitude= Depending on the altitude the Inspired Fraction of Oxygen is less than at sea level, no problem if the lake is at sea level altitude
Visibility= At least in our lakes, visibility is awful, you should pay more attention to security and probably need to use some kind of ilumination.

My advice is that don't extrapolate, just take it easy at the beggining and progress in depht as you feel comfortable

Fresh water is approximately 2% lighter for the same volume. Like Frank says, the viscosity is lower, although I haven't noticed much difference. If your depth guage is calibrated for salt water, you will actually be 2% deeper than it indicates. Interesting side effect, but probably not enough to make a noticable difference. One thing that might be significant is the amount of wet suit you are wearing. Assuming you are diving in Florida springs, the temp is like winter in Palm Beach. More wetsuit may cut your depth range. Being cold sure will. If you plan to dive Blue Springs, the current and cave effect trumps all of this. Where are you heading?

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