From our local Nature Conservancy (and fellow geocacher) I found
the following:
The Marre Weir (dam) dates back to the 1960's and was installed
to keep saltwater from infiltrating freshwater wells upstream. The
weir, however, was identified as a partial barrier to migrating
steelhead trout. An existing fish ladder helped but was often
clogged with debris. The principal problem at this location was
that the weir delayed fish migration as fish wait for favorable
flow and tide conditions. Time delays can prevent fish from
reaching spawning areas during optimum spawning conditions. The
Land Conservancy's solution to this problem was to work with the
owners of the weir to improve an existing opening to allow better
fish passage with less debris accumulation. The project is not
anticipated to impact salinity levels upstream, but monitoring in
coordination with the weir owners is planned. The project works in
both high and low tide conditions by concentrating flow to attract
fish. The concentrated flow also makes a deep pool on the
downstream end which helps fish attain better launch speeds to jump
through the opening.
Looking upstream at the Weir prior to
construction.
The existing opening was often blocked during the fish migration
season.
After construction, the new opening
concentrates low flow to form a passageway. The wider top is
intended to allow larger objects floating downstream to pass
through.The opening will stay open during the fish migration season
based on the terms of a maintenance agreement negotiated with the
weir owners.
During the summer season when fish are not migrating, the weir may
be closed to
impound water as it has for the last 40 years.
For more information about our local steelhead trout, see
this
article from the Santa Barbara Audobon Society.