Most of the culverts we drive over today were built decades ago before we knew about the needs of these species. Ability to migrate upstream is a critical issue for both anadromous and resident fish species. They can't jump as high or sustain the same bursts of energy, and they're more sensitive than adults to turbulence and to changes in water temperature. In the Pacific Northwest, the fish-passage issue is complicated by biology. Pacific salmon, unlike Atlantic salmon, exist as several species.
Different populations spawn at different times and in different streams.
What's more, Pacific salmon spawn only once and then die. Populations have declined to such an extent that virtually all stocks of wild salmon and trout are federally listed in some region of the Pacific Northwest. For example, Chinook salmon stocks are federally listed in Puget Sound, in the Columbia and Sacramento Rivers, and in other watersheds. Under the Transportation Equity Act for the 21st Century, or TEA-21, Federal Highway Administration funding support is available for wildlife crossings on both new and existing roads.