Even our retention ponds down here have wildlife or wildlife that frequents the water. I won't get graphic but you can see where I'm going with that. The fountains are usually to keep the water from getting stagnant and to reduce mosquitos. The water can get quite warm, however we've had lots of rain so not sure about water temp. I do know that come winter these ponds lose a lot of water because it very rarely rains here in the winter months. As far as determining drowning-circumstances play alot into it because there's a big debate among medical examiners about water in the lungs being inhaled but the person is unconcious versus a prolonged submersion and water leaking in.
There are 2 retention ponds on Bella Vida-it's a cul de sac, still being developed, lots of dumpsters, half built homes, empty homes and empty lots. PS Thanks for scoping that out FLbeachdawg!