The Gowanus Dredgers produce an annual schedule involving living along the Gowanus Canal. The last event of the 2004 season allowed people to explore the canal in a canoe, which doesn't happen that often as the canal is normally not open to the general public.
They had a race later but I didn't stay to watch, even though people would be bringing anything that could float.
A larger photo gallery is available. As well, one of the other guys in my canoe was the Brooklyn Vegan, who took his own pictures of the canal.