The Malibu Creek Watershed covers more than 100 square miles of mostly undeveloped land, from Agoura Hills and Thousand Oaks across the Santa Monica Mountains, to where it drains into the Santa Monica Bay. The area is generally thought of as being mostly pristine. But a large study by the group Heal the Bay says humans have caused pollution and other problems throughout the watershed.
Heal the Bay has released a study based on 12 years of research by its staff and citizen volunteers. It finds pollution from runoff, along with other problems, far up into the watershed. “There are places here that are quite healthy," says study co-author Sarah Sikich of Heal the Bay. "But we found evidence of degradation most likely related to development in the watershed, habitat damage from hardened streams and other issues.”
The report found invasive species, including crayfish and New Zealand Mud Snails, in Malibu Creek.
Heal the Bay also discovered excess levels of nitrogen and phosphorous in the creek. Heal the Bay co-author Katherine Pease says an imbalance of these chemicals in creek water leads to too much algae.
“When we have high algae what can happen is it creates poor habitat for aquatic life,” she says. “If you get too much algae it will just proliferate and then as it decays it uses up all the oxygen in the stream.”
The nitrogen and phosphorous come from the Tapia sewage treatment plant, and from city streets in places like Thousand Oaks.
Heal the Bay’s research has already had an impact: it influenced stormwater rules for new developments. Those rules promote capturing rainfall for reuse or treatment, and are in effect in LA and Ventura counties.
Study co-author Mark Gold, now at the UCLA Institute of the Environment and Sustainability, says existing development contributes to the runoff problem too. “That, frankly, on stormwater, not just within this watershed, but really nationwide, is the biggest water quality challenge,” he says.
Heal the Bay's report has several recommendations. Some apply to the public, like asking hikers to freeze their boots to kill possible invasive snails before going hiking in the Malibu Creek watershed. Others are directed towards government agencies and large public projects: the study advocates the removal of the old Rindge Dam, now silted in for more than 60 years.
The Santa Monica Bay Restoration Commission’s Shelly Luce, another co-author, says the dam keeps steelhead trout from swimming upstream, and keeps sediments from flowing to the sea.
“When boulders and cobbles especially make it all the way down to the coast they form things like surfbreaks and reefs that kelp can grow on.,” she says.
Luce says she hopes the report will help promote the idea that the watershed is connected to the coast, and human activity is connected to the watershed.