Badly damaged Topanga Lagoon in Malibu has a chance to be restored

As motorists whir along the nearby Pacific Coast Highway, throngs of tidewater goby and steelhead trout—two species of endangered fish—find refuge in the vibrant, albeit severely deteriorated, Topanga Lagoon.

The lagoon, an area where freshwater from Topanga Creek and seawater mix, is less than one acre in size and is nestled along a stretch of the Santa Monica Bay. But what has long been whittled away was once an expansive wildlife haven, 30 times its current size.

After more than...