In many states police and fire emergency workers are barred from suing under what’s called the rescue doctrine. The idea is that it’s not good public policy to make people afraid to call 911 because they’ll be liable if any of the professionals who respond are injured. The doctrine doesn’t apply to hidden, unusual dangers unless the rescuers are advised of the risk, like having kegs of black powder in a house that’s on fire. Water around a drowning victim probably isn’t hidden or unusual. But don’t count on the case being thrown out-frivilous lawsuits are only filed because they are sometimes successful.
My guess is some scumbag lawyer is going for a settlement that's cheaper than the costs to insurance company (ie. paying its lawyers) for defend the suit. This cop will likely get $10-20K.