California's Water: Cleaning Water the Natural Way

Wetlands have always been a key ecological resource in California. In addition to providing habitat for thousands of species, they play a key role in cleaning urban runoff before it reaches estuaries, beaches and the ocean.

This segment of “ California’s Water” explores how wetlands serve as nature’s own water filtration systems. A visit to the San Joaquin Marsh in Irvine offers a first-hand look at the valuable function wetlands areas perform in removing pollutants from runoff while at the same time providing habitat and recreation opportunities.


With their unique ability to remove nutrients and pollutants from runoff, wetlands are enormously beneficial to both people and the environment. Unfortunately, California has lost as much as 95% of its natural wetlands over the decades as the state has developed. As a result, we are missing out on nature’s ability to clean and naturally filter out pollutants from urban runoff before it reaches our bays, our beaches and the ocean.

Luckily, many local water agencies are seeking to change that through collaborative efforts to restore wetlands. By acquiring and reconstructing natural wetlands areas, local agencies are helping to recreate nature’s way of cleaning water, while at the same time providing valuable habitat for species and new recreational and education opportunities for their communities.

A prime example is the San Joaquin Marsh in Irvine. Through collaborative partnerships, Irvine Ranch Water District has restored much of the marsh to natural conditions – with benefits for the San Diego Creek watershed and Upper Newport Bay.

Today, the reconstructed wetlands form a flow-through system allows water from San Diego Creek (which receives water from urban storm drains) to be pumped into the wetland ponds. There, the water slowly moves through the ponds for seven to 10 days. During that time, the water comes into contact with cattails, bulrush and other vegetation that helps remove 50% to 70% of the nitrogen in the water. Too much nitrogen in local streams can lead to algae blooms in Upper Newport Bay, resulting in lower oxygen levels for fish and other aquatic species.

The water quality benefits of San Joaquin Marsh have worked so well over the past seven years that Irvine Ranch Water District is now working to build 31 smaller wetlands throughout the San Diego Creek watershed. The first four sites of the project have already been completed and planted with native vegetation, and design work is under way on the additional sites. The project is called the Natural Treatment System.

The marsh is also the site of IRWD’s San Joaquin Wildlife Sanctuary, which is home to more than 200 species of birds and other wildlife. Blue heron, egrets, tree swallows, black skimmers and a variety of ducks are commonly seen. The sanctuary’s 12 miles of walking trails attract bird watchers, wildlife photographers and others seeking to enjoy this unique setting in the midst of an otherwise urban area.