Lightning doesn't generally strike water. However, you are in a pool, everything is wet, the pool is likely surrounded by, oh, chain link, light poles, assorted targets. Lightning strikes, water transmits electricity, you get fried. I've been as close as 10 feet to a lightning strike. I love lightning, I've studied it, and it scared the shit out of me. Lightning is far more powerful than you can even imagine.
Would it kill the life in the pond? Probably not. Apart from the fact that it likely would't strike the pond (lightning tends to strike the highest or most attractive object in any give area) the electricity would skim the surface, basically, looking for the closest ground point. Water is a conductor, not a ground.
