Publication Summary

Washington state law requires that instream resources and values, including fish, are protected and preserved with adequate stream flows. One of the most important water management tools we have to protect stream flows is to set stream flow levels by regulation, called "instream flows."

To determine stream flow numbers, a lot of discussion centers on fish needs. This is because fish are considered an "indicator species" – if the fish are doing well, then generally other instream resources are too. And fish needs can be more easily quantified by existing methods than other instream values. This is why fish studies are often the basis for determining instream flow numbers.