I heard in the past they would occasionally drain it and clean out the stuff dumped in there and that was always interesting...the stuff that was hiding under the surface...like a washing machine I thought I heard?
'96-'98 ish they drained or dredged it, happened to be walking by it early on a weekend morning for some reason (can't think of why), ended up with a cool old schwinn bike. Guy working said he had pulled it out that morning, hadn't been in there long.