Dave -- we just carry around a conductivity meter -- very simple. Put a probe in the water, and take a reading. I think the measurement is resistance between a couple of copper lines in the probe. The units are microsiemens/cm, but used to be micromhos/cm before the physicists changed the name. I'm sure it's related to alkalinity/total dissolved solids (I generally don't usually measure alkalinity up here, as we always have "plenty"), as the higher the dissolved solids (the more "stuff"/nutrients/salts/etc.), the more the resistance in the water. So, distilled water is a very poor conductor of electricity. As you add salts (dissolved solids, etc.) then the water can more easily carry some current. So low conductivity is hard to electrofish. If you add a lot of salts, then you get too much resistance, and it's again hard to electrofish because the generator can't supply the needed power against the high resistance. In eastern SD, the lowest water conductivity in which I sample has a conductivty of about 320, and I've "tried" to sample in water over 4,000. I suspect Greg was probably dealing with water that had a conductivity of 10 or even lower, which makes it very hard to get a sample of fish. Electrofishing is most effective (at least theoretically) at a conductivity near that of a fish body. In general, most fish have a conductivity of roughly 150. That's when the most current flows into the fish body, because it's the same as the surrounding water. Well, is that overkill or "education time?"
