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Arroyo Seco Project

The Arroyo Seco is a tributary to the Los Angeles River that originates in the San Gabriel Mountains and flows south through Pasadena. The City has the right to divert up to 25 cubic feet per second (cfs) of water from the Arroyo and spread it in basins for groundwater recharge. In our on-going effort to increase overall supply reliability, PWP will be taking steps to fully utilize this existing water right to maximize local water resources and reduce dependence on imported water supplies.

PWP has existing diversion facilities in the Arroyo Canyon. Over time, the facilities have fallen into disrepair. Then, following the 2009 Station Fire, flooding from the 2010 winter storms caused further damage to PWP’s infrastructure.

The Arroyo Seco Canyon Project (ASCP) will take a multi-benefit approach to improving PWP’s water resources by addressing the shortcomings of its existing infrastructure, while also enhancing the natural habitat and the recreational experience for visitors of the local trail system into the Angeles National Forest.


Following the requirements of the California Environmental Quality Act (CEQA), an Initial Study and Mitigated Negative Declaration (MND) were prepared for the ASCP. Shortly after the environmental documents were adopted in 2015, a lawsuit was filed against the City. In June 2017, the court found that certain project elements were inadequately analyzed under CEQA, and ordered the City to partially invalidate approval of the Conditional Use Permit and the MND.

On July 24, 2017, the City Council rescinded its approval of those parts of the project related to increasing capacity to take water from the Arroyo. Per the court’s judgment, PWP will not be able to proceed with these improvements to its water infrastructure until they are further analyzed in an Environmental Impact Report. The City is currently evaluating the feasibility and scope of the project, as it plans for its next steps.