Culverts placed under roadways, whether county, city, or state highways are designed to allow the drainage of land to occur while maintaining transportation viability. A less thought of purpose for culverts is to allow fish migration up streams to their spawning grounds. Culverts are a benefit in this way, as without them roadways would block or divert these flows of water.

But, how can culverts have a negative impact on fish passage?

High Water Outlet
If the water outlet is too high above the stream, then migrating fish are unable to jump up into it to continue their movement upstream.

Steep Incline Of Culvert Itself
A culvert placed under a section of roadway at too steep of an incline could force the water to flow too fast and the fish to be unable to swim against the flow to continue their migration.

Shallow Depth Within Culvert
Sometimes if the water depth inside the culvert is too shallow, the fish are unable to completely submerge their bodies and swim through it.

Debris Blockage
If the culvert is blocked at either end by debris like rocks or fallen trees, this too would make it unpassable to migrating fish.

Properly placed culverts not only do their job in diverting water flow and flood damage, but also allow fish to migrate in as much of a natural way as they can.

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