Dave B. I don't think the thick mats of filamentous algae will have a big impact on the success of bgill spawning in your lake. Keep in mind that the male fish builds, guards and keeps the bowl, shaped, nest area clean during the egg laying, incubation & hatching, and until young leave the nest. Once the young fish leave the nest, the occasional fish probably gets entangled in algae mats but I think the majority are able to avoid entanglement and a very low percentage of deaths occur.
One exception to this opinion - Hydrodictyon (High-drow-dick-ton). This is a green filamentous algae that is commonly called "fish net algae". It has the appearence and shape of a fish gill net. Small fish try to swim through it and get caught / entrapped in the openings by the gills and soon suffocate.
