if it's a gas plant and not coal-fired it would be much cleaner. you'd still get the chemicals they put in to treat the water, but you'd have a lot fewer heavy metal problems and you'd completely avoid the run-off from the coal pile.
as powerplants go I'd live next to a gas fired if I had to choose one. (as long as they didn't switch to oil too often, most plant around here only keep a supply of oil on hand to maintain electric service in the event of problems with the gas line)
and they do not drain the boilers into the lake(anywhere).
when the boilers are shut down for inspection/repair (anually at the very least, unless safety codes are much more lax in Texas). the boilers are drained. then after repairs they are hydro-staticly tested (this involves filling them with water and applying pressure, sometimes filling and draining several times before all leaks are found and fixed), then draining them. then they are filled with water treated with a caustic chemical and 'boiled down' (to remove impurities) then drained. the original water is chemically treated and the boil-out water is also treated, they are drained right out onto the floor, into the storm drains and out into the cooling pond.
in a gas plant you'd only have this a couple times a year though so it would be fairly minimal if it's a good sized lake.
