These attempt to keep fish out of the water diversion by causing the fish to swim away from the site. Commonly used materials include perforated plate, woven wire mesh and welded wedge wire. Presently, these are the only fish screens that meet DFG fish screen criteria. Fish screens are necessary to prevent the loss of fishery resources at water diversion sites. Instead, several once-abundant fish populations are now listed as either threatened or endangered under either the Federal Endangered Species Act, or the California Endangered Species Act.
State law provides the authority for the installation of fish screens.
This authority is described in several sections of the Fish and Game Code. Screening requirements vary, depending on the age and size of the diversion. For diversions constructed or modified since 1972, Fish and Game Code Section 6100 et.seq, apply. The diversion must be screened if, in the opinion of the DFG, it will affect either salmon or steelhead. For diversions installed before 1972, either of two other Fish and Game Code sections applies, depending on the size of the diversion.