They reckon the algae on the pontoon attracts small fish,same under piers and docked boats.
Watched a vid on it,the guy was using a light under water,the algae was attracted to the light (mock sunlight)The next form of algae were attracted to the initial algae,small fish were attracted by that,and then the predators.He was on a big lake in the states.
They filmed the fish buildup under water,it only took an hour for the big fish to turn up.