A couple weeks back on a hot Saturday or Sunday, it was pretty well packed on the beach and in the water, including kayakers [[you can rent a kayak near the DYC and use it in the area).

This article from Crain's Detroit Business discusses the water quality of the beach and what beachgoers have to say:
Detroit no longer tests water at Belle Isle Beach because of cost
http://www.crainsdetroit.com/article...ecause-of-cost