Yes Jules, they do help keep the water cooler, and they also use up nitrates, meaning less chance of the dam turning into pea soup. The blocking of light by the big leaves also lowers the light levels, which helps reduce algae growth as well.
jules wrote:You might find something friendly in a nearby creek.
I suspect that would be illegal, better to collect seeds if you know what it is, or buy a known non-invasive plant from a nursery.
Jimbo, since they like to be under a small depth of water, I guess they'd have to relocate lower down the slope as the water recedes. I'm not sure what their ideal water temp range is, but as the water gets very low, it is likely to become too warm for them.