These three corrugated metal culverts outside of Centreville, MD, at a road-stream crossing are a severe barrier to fish migration, says Julie Devers, fish biologist. Water flows through the crushed and rusted pipes to drop into a shallow pool at the outlet. If fish were trying to swim upstream to their spawning grounds, they would be forced to jump, an impossible task for migrating fish species found in this watershed. Credit: Steve Droter

These crushed and rusted pipes are a severe barrier to fish passage along this Maryland road-stream crossing. Credit: Steve Droter