Early in our history,
rivers ran wild, and fish followed them according
to their needs. This was
a time when our fishery resources
seemed abundant and without end.
Since then, millions of culverts, dikes, stream diversions, dams,
and other artificial barriers were constructed for transportation, to
impound and redirect water for irrigation, flood control, electricity and
drinking water. Many of these alterations have changed the open access
features of rivers and streams and have taken their toll on our fishery
resources. Improperly designed or damaged stream crossings are by far the
most common cause of these problems.
~ Restoring fish
passage benefits people, fish and the environment ~
The vast majority of
crossings are culverts or bridges on small streams. Nearly all culvert
installations are intended to serve the purpose of providing vehicle
access, however, many also have an unintended function- they can block the
migration of fish up or down streams.
They also alter the geomorphic processes by which river channels
form and maintain habit over time. For example, they may block or
constrict the passage of sediment and large wood being transported by the
river, and prevent channel migration.
movements within streams are vital for maintaining healthy populations.
Spawning migrations like those made by trout and salmon may be the most
visible and dramatic, but seasonal (or even daily) movements upstream or
downstream to find food supplies, refuge from predators, preferred
temperatures or cover may also be critical.
Where fish habitats are divided into small segments (fragmented) by
man-made barriers, whole populations may be eliminated, reduced or
genetically damaged through the effects of isolation and inbreeding. The
consequences can be disastrous for fish populations and other aquatic
organisms within a watershed. It is a fundamental fact, fish need to move.
For example, many fish need to move between feeding and spawning areas and
make other seasonal movements to important habitats.