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<p>Over 95% of California’s wetland area has been lost to urbanization, prompting efforts to restore Los Angeles County’s Ballona Wetlands Ecological Reserve. Adjacent to the reserve, the Ballona Freshwater Marsh was constructed in 2003 on former agricultural land to mitigate urban and stormwater runoff. This study presents a two-decade analysis of the marsh’s effectiveness in reducing enterococci concentrations, a leading indicator of pathogenic water pollution. <i>Enterococcus</i> spp. levels from the marsh’s main inlets and outlet, recorded between 2005 and 2025, were compared to determine filtration efficacy. Results indicate the marsh often removes enterococci and can lower bacterial counts to safe levels. The geometric mean of the outlet-to-inlet ratio was 0.322 (95% CI: 0.259–0.399, p &lt; 0.001). However, removal is not uniform, and increasingly the marsh behaves as a source rather than a sink. The California Department of Fish and Wildlife (CDFW) plans to restore 566 acres of the Ecological Reserve by removing cement levees and rerouting the adjoining Ballona Creek through a meandering path to recreate an ecologically active estuary. Separate analysis of water from the Ballona Creek over the last six years shows levels of pollution regularly above the Environmental Protection Agency (EPA) safety thresholds for fecal bacteria. This paper suggests water quality improvements if the restoration proceeds.</p>

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A twenty-year analysis of the ballona freshwater Marsh’s removal of fecal bacteria from municipal runoff

  • 期刊论文

  • 发表日期：

    2026年3月29日

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  • Annalia J. Henderson

摘要

Over 95% of California’s wetland area has been lost to urbanization, prompting efforts to restore Los Angeles County’s Ballona Wetlands Ecological Reserve. Adjacent to the reserve, the Ballona Freshwater Marsh was constructed in 2003 on former agricultural land to mitigate urban and stormwater runoff. This study presents a two-decade analysis of the marsh’s effectiveness in reducing enterococci concentrations, a leading indicator of pathogenic water pollution. Enterococcus spp. levels from the marsh’s main inlets and outlet, recorded between 2005 and 2025, were compared to determine filtration efficacy. Results indicate the marsh often removes enterococci and can lower bacterial counts to safe levels. The geometric mean of the outlet-to-inlet ratio was 0.322 (95% CI: 0.259–0.399, p < 0.001). However, removal is not uniform, and increasingly the marsh behaves as a source rather than a sink. The California Department of Fish and Wildlife (CDFW) plans to restore 566 acres of the Ecological Reserve by removing cement levees and rerouting the adjoining Ballona Creek through a meandering path to recreate an ecologically active estuary. Separate analysis of water from the Ballona Creek over the last six years shows levels of pollution regularly above the Environmental Protection Agency (EPA) safety thresholds for fecal bacteria. This paper suggests water quality improvements if the restoration proceeds.