The farming forum post replies have feedback on when PP required, when building regs get involved etc, pitfalls (eg stream next to lake, fishers dont want to pay for local otter to eat all the fish :-) mind you that could be an attraction in itself).
But short answer is yes it would be change of use if you are charging people to use it and yes it would require PP. Really the only exemption is a smallish one (certainly less than 1 acre - the FW article recommended min 3 for a commercial lake) which is for agric purposes or own enjoyment - anything bigger or commercial would need PP.