Be real careful when boating in the bay's upper reaches. The good folks at Conowingo Dam dumped a lot of flotsam over the spillways last week, trees, logs, barrels, things that could easily sink your boat if you hit them. Early last week there was 10 acres of junk just above the dam, and the following day a couple spillways were opened and that 10-acre pile of debris was reduced to just under a half-acre. Now there are logs in the marina the size of telephone poles. So much for the Chesapeake Bay Cleanup Program.