Physical Barriers

Animal movement can be blocked by clogged or collapsed culverts. Also, weirs or baffles, which are typically designed to increase depth or decrease velocities within a crossing structure, can create barriers for some weak swimming or crawling species.

As rigid structures that typically constrict the natural stream channel, crossing structures can trap debris is such a way that blocks or inhibits aquatic organism passage. Beavers often find these undersized structures to be convenient places to dam up streams. Larger structures are not only more likely to pass woody debris but are also less likely to be blocked by beavers.