Strange things can be found in the area’s rivers, from frankenfish upstream and downstream, to things like USA Today distribution boxes and a Civil War-era sword (as recovered during the recent Capital River Relief clean-up.) Now add blue barrels.

WTOP reports that near Great Falls and other places, more than 50 sealed blue barrels have washed ashore. And they’ve been found in other areas of the Potomac and the Anacostia.

Environmentalists say while both rivers have had these mysterious blue barrels wash up over the years, their numbers recently have increased dramatically.

So what could they be? According to WTOP, environmentalists believe they could be used for floating docks.

(Photo of WTOP’s Mark Segraves by Patricia Xavier)