I live considerably upstream in the Los Feliz area just west of the Golden State Freeway and a little north of Los Feliz Boulevard.
Fifteen years or so ago my children and I used to spend a bit of time in the Los Angeles river bed. We would look for frogs' eggs in the spring. Usually the river bed turned black as the eggs hatched and turned into polliwogs.
Later the Army engineers put up a high chain-link fence and we could no longer get down to the river bed.
In the winter rainy season I still stop by to watch the muddy flood waters go swirling, sometimes 14 feet deep. The river can rise almost overnight and subside as quickly. Someone has painted nice cat faces on the manhole covers to the storm drains, which prevent the flood waters from backing up into the streets in the Atwater neighborhood.