Fish Passage

Potential permits required: CWA 404, Threatened & Endangered Species, NHPA, Floodplain


Providing fish passage along a stream corridor creates a healthy ecosystem that allows the migration of fish and other aquatic organisms upstream and downstream during different times of the year for feeding and spawning activities. Installing Fish Passages allows lasting benefits such as:

• Providing fish/aquatic organism passage
• Providing healthy, connected ecosystem
• Providing recreational values

Fish passage barrier on the Big Thompson River.

As discussed in the aquatic species section of ‘Chapter 2: Evaluating Your Property’, fish and other aquatic organisms depend on the connectivity of a stream corridor to thrive. Along a stream system, there are many potential fish barriers. Incorrectly designed drop structures, culverts or crossings can be fish barriers. Similarly, dams or irrigation ditch diversions can be fish barriers. In order to fix this issue, there are a variety of solutions that will be dependent upon the situation. Engineers, landscape architects, environmental consultants and/or river constructors can help you decide the best path forward.

Because the existing fish barrier could come in the form of a dam, diversion structure, culvert/crossing or a point that dries up, there can be major impacts to the floodplain and ecosystems. Incorporating fish passage or fish ladders into an existing stream can require extensive grading and potential modifications of existing structures, the channel and the floodplain. Fish ladders, which are a specific fish passage technique, can be very large and require a structural evaluation and design as well.

Fish passage can also often be incorporated into an existing crossing structure to ensure the fish can move beyond the structure. There are multiple approaches to doing this, depending on the existing conditions of your culvert/crossing.

When discussing fish passage options with outside resources, it will help to know the types of fish that live in your stream system. Each fish species has unique characteristics that determine how they move upstream. For example, the distance a fish can jump vertically can vary greatly between species. Other criteria include how deep the water must be, the temperature of the water and how fast the water can be moving. After determining the types of fish to design for, the outside resources should evaluate different options and discuss how they will impact existing structures, ecosystems and the floodplain.

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