ISI screens arguably provideS the highest level of fish protection of any technology available IN THE MARKETPLACE today

Achieving Fish Protection

A key benefit of the ISI screen system is that we can build screens with the smallest opening sizes available (down to 0.5 mm and potentially smaller) and include a large screen surface area in a small footprint to achieve low approach (0.2-0.4 fps; 6.1-12.2 cm/s) and through-screen velocities (0.3-0.8 fps; 9.1-24.4 cm/s). The elements of screen opening size and velocity are the key elements regulators rely on to achieve fish protection as an appropriate combination of these factors can provide both mechanical and hydrodynamic exclusion of the smallest fish eggs and larvae to the largest fish, turtles, and marine mammals. The key differentiator of our system is that the mechanical brush cleaning system maintains a clean screen surface and thus allows use of the smallest screen opening sizes available and maintains velocity criteria by not allowing debris or biofouling on the screen surface.

Perhaps the best evidence of our proven ability to provide the highest levels of fish protection is that ISI has completed more than 200 projects in designated critical habitat for sturgeon and salmon, all of which were approved by state agencies as well as either NOAA Fisheries or the US Fish and Wildlife Service.

Fish Screen Criteria and Regulations

Fish screen criteria are variable across the United States and around the world resulting in no one-size-fits-all screen design. Each screen project should work to understand what fish protection requirements apply and then engage with regulators to obtain approval of the final screen design. Projects in the United States that have the potential to impact federally listed species or are located in listed species designated critical habitat will need to gain approval from NOAA Fisheries or US Fish and Wildlife Service as well as state regulatory authorities. NOAA Fisheries has jurisdiction over marine and anadromous species while USFWS has jurisdiction over freshwater and catadromous species.

Some US states have developed criteria, policies, or regulations that apply to fish screens located in those states. There are also federal regulations related to cooling water intakes which are regulated by EPA and those state agencies which have been delegated authority to issues National Pollutant Discharge Elimination System (NPDES) permits. These cooling water regulations fall under Section 316(b) of the Clean Water Act and apply to all US states and US territories. States are required to be at least as stringent as the federal Section 316(b) regulations. For international locations, Canada and the European Union have developed and continue to develop fish protection requirements at water intakes. Most other locations regulate on a site-specific basis or not at all.

Below are links to US state and federal and international resources that can be used to guide the design of projects. Given that screen criteria and regulations are constantly changing and the broad discretion is typically given to regulators, we recommend the below only be used as a general guide to potential requirements at a given site. ISI is familiar with regulatory design requirements and can assist in the selection of an appropriate design for your project.


NOAA Fisheries

NOAA Fisheries Screen Criteria were updated in 2022 and provide fish screen design guidance for projects in Washington, Oregon, Idaho, and California. Refer to Section 8 – Fish Screen and Bypass Facilities for more details.


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