strainer
n.— «Sweepers—clumps of branches or roots that hang out over the water or jut up out of it—are to be avoided. They are dangerous. The current can pin a person against them. In a worst-case scenario, sweepers can push a person under water and hold them there stuck in what is called “a strainer’” until they drown. The Kenai has claimed more than a few lives this way, as have other Alaska rivers.» —“PFD can be a lifesaver if you bother to wear it” by Craig Medred Anchorage Daily News (Alaska) July 8, 2007. (source: Double-Tongued Dictionary)
Further reading
A retronym is a word coined to distinguish something new from an older, more generic version, such as electric guitar or clock radio. A couple of new retronyms are fine water, or “unprocessed water that reflects a region’s terroir” and water...
Strainer – a naturally occurring device for straining careless kayakers and canoeists out of a river.