By hello
A concrete gravity diversion dam on the Sacramento River, built in 1962–1964 for irrigation. It is formally decommissioned, and its gates are now left open year-round so the river can flow freely through the site, a change driven by long-running fish-passage problems for salmon and other migratory fish. (en.wikipedia.org) Notable detail: 11 large gates once formed Lake Red Bluff for gravity diversion. (usbr.gov) Why it remains: irrigation diversion was shifted to pumping-based solutions rather than immediate total demolition of the structure. (usbr.gov) Further information: https://www.usbr.gov/projects/index.php?id=244 https://www.usbr.gov/mp/TFFIP/red-bluff.html