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October 4, 2022  |  Written by Michael W. Daugherty

Colorado Water Quality Control Division Proposes New Nutrient Water Quality Standards for Lakes and Reservoirs Across the State

The Colorado Department of Public Health and Environment’s Water Quality Control Division (WQCD) has proposed significant revisions to the nutrient water quality regulations for lakes and reservoirs across the State. The proposed revisions seek to tighten nutrient restrictions for lakes and reservoirs that have a public health nexus — water bodies with public swim beaches and that serve as drinking water supplies — immediately, and those with aquatic life, recreation, and/or direct use water supply uses by 2027. A public rulemaking hearing is scheduled before the Water Quality Control Commission (WQCC) on April 10, 2023.

Federal Direction to Enact More Protective Standards to Limit Algal Blooms

The decision to seek stricter water quality standards for the State’s lakes and reservoirs is a direct response to federal pressure to enact more protective standards and stems from concern over an increase in harmful algal blooms in the State’s waterways. In 2012, the WQCC adopted interim standards for chlorophyll a, phosphorus, and nitrogen intended to limit the overabundance of algae. In 2016, the United States Environmental Protection Agency (EPA) declined to approve all the WQCD’s interim standards and directed the WQCD to revisit its standards and classifications to determine whether they adequately protect lakes and reservoirs. As a result, in 2017, the WQCD announced a 10-Year Water Quality Roadmap that outlined strategies for developing nutrient criteria and other water quality priorities over ten years from 2017 to 2027.

The standards proposed by the WQCD in this rulemaking are a result of the EPA’s action letter and attempt to secure EPA approval, which determines whether the State’s nutrient standards become legally effective for Clean Water Act (CWA) purposes. See 40 CFR § 131.21. If unconvinced that the WQCD’s revised nutrient standards will adequately protect lakes and reservoirs, the EPA could promulgate replacement federal nutrient standards for Colorado surface waters pursuant to CWA § 303(c)(4)).

Rulemaking Hearing Delayed in Response to Party Pushback

The WQCC’s notice of public rulemaking issued on July 12, 2022, initially set the hearing date as November 14, 2022, which provided potential parties with approximately one month to evaluate the WQCD’s proposal and determine whether to participate in the rulemaking as a formal party, two months to submit a responsive prehearing statement, and four months to prepare for a public rulemaking hearing. In response to the short timeline, multiple parties moved to extend these dates. In response, the WQCD proposed a six-month delay of the rulemaking schedule, proposing a new date of April 10, 2023, for the rulemaking hearing. Following a public status conference, the WQCC adopted the WQCD’s proposed timeline and added a deadline for the WQCD to submit a supplemental prehearing statement by October 5, 2022.

Forty-seven (47) parties—including cities, towns, special districts, water quality authorities, private corporations, technical groups, and State agencies—have joined the rulemaking as formal parties. Some of the primary concerns with the proposed nutrient standards include how they will affect end-of-pipe permitting and whether the data relied on by the WQCD supports them. These entities will continue to negotiate with the WQCD until March 16, 2023, at which point parties with outstanding issues will prepare for the public rulemaking hearing.

If you have any questions about this rulemaking or water quality regulations in Colorado generally, please contact Michael Daugherty at for more information.

Somach Simmons & Dunn represents the Chatfield Watershed Authority in this rulemaking.

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