Protecting Cold Water Resources in Maryland

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​​                                    Photo courtesy of the Chesapeake Bay Program

This page serves as a​​​n information hub for all current MDE guidance, policies, ongoing work, and resources for cold water protection.

Cold water streams in Maryland are a vital resource for aquatic communities that rely on lower temperatures to thrive. Identifying and protecting the thermal regime of these stream environments is crucial for supporting vulnerable cold water species. These species include Maryland’s native brook trout, recreationally important populations of rainbow trout and brown trout, and two cold water obligate benthic macroinvertebrates (Tallaperla and Sweltsa). The Strategy for Protecting and Restoring the Chesapeake Bay Watershed, Executive Order 13508, further identifies the brook trout as a key indicator species for Maryland’s waters, reflecting overall stream habitat health and holding great ecological, commercial, and recreational significance. 

Maryland designates and protects cold water streams under the federal Clean Water Act, identifying them as Use Class III (nontidal cold water use), or Use Class IV (trout-stocking waters). Growing concerns around climate change and warming temperatures highlights the importance of protecting these valuable cold water resources in Maryland. Elevated water temperatures due to climate change will limit the available cold water habitat for dependent species, threatening their populations. Increased development in the watersheds of cold water streams or best management practices (BMPs) lacking cold water protections can compound the problem, contributing to higher influxes of warm temperature stormwater runoff into vulnerable cold water streams. Water quality standards in conjunction with strategies to best manage and mitigate high temperatures are therefore critical to the survival and health of cold water communities.

Where are cold water resources located in Maryland?

Most of Maryland’s cold water resources occur from the Piedmont geological formation and to the west of the state. Maryland’s cold water resources are described in several ways.  First, Maryland’s water quality standards describe cold water resources in terms of “designated uses” with Use Classes III, III-P, IV, and IV-P being those that require cooler water temperatures as water quality criteria.  Recently, MDE has also recognized several waters with cold water existing uses which may not have a Class III or IV designation yet but which exhibit characteristics consistent with a cold water stream.  To view Maryland’s designated cold water uses and those streams with cold water existing uses, please view MDE’s designated uses map.  Another mapping resource provided by the Maryland Department of Natural Resources is the Cold Water Resources Mapping Tool​​.  This dynamic map provides information including but not limited to: watershed coverages for areas with existing cold water resources, layers showing waters that are stocked with trout, and priority watersheds for brook trout restoration.

What Water Quality Standards are there for cold water resources?

Maryland has different use class designations for cold water streams in Maryland that provide protection to these resources. Streams designated as Use Class III (or III-P) waters (nontidal cold water use) provide the most stringent temperature criteria, requiring temperatures to stay below 20°C.  Use Class IV (or IV-P) designations (recreational trout-stocking waters) also represent cooler water resources and have a water temperature criterion of below 23.9°C. For more information on Maryland’s designated uses, please click here

Some Maryland streams do not meet the stringent temperature requirements of a Class III designation, but have demonstrated cooler temperature regimes and/or the presence of naturally reproducing cold water obligate species that the Class I (warmwater aquatic life) or Class IV (trout-stocking waters) designations do not protect. The cool or cold water temperatures and biological conditions within these streams demonstrate an ‘existing use’ that is different from the current designated use. To ensure that these waters receive adequate protections, a policy and procedure​ was developed to formally recognize these waters as having a cold water existing use. These existing use determinations, along with the corresponding data and rationale, are provided for public review and after that review, are finalized on MDE’s Existing Use Determinations webpage. Waters with formally identified existing uses are then afforded the necessary protections for their maintenance under their described thermal conditions.

MDE, along with its partners on the Cold Water Advisory Committee​, will be considering and working on other revisions to water quality standards so as to improve the accuracy and protection of Maryland’s cold water resources. For more information about this ongoing work, please see the Cold Water Advisory Committee homepage.  To learn more about MDE’s Existing Use Policy and Procedures, click here​. ​

Does Maryland assess the health of cold water streams?

MDE is responsible for assessing the State’s surface waters in compliance with Sections 303(d), 305(b), and 314 of the Clean Water Act.  To meet this requirement, every 2 years, MDE develops the Integrated Report of Surface Water Quality.  This report provides assessment results on those waters for which data are available based on whether a water body is meeting water temperature criteria or not.  Water temperature data collected for this purpose must be collected according to the protocols described in the MD DNR Quality Assurance Document for Temperature Monitoring.  Data that meets this quality assurance threshold are then assessed according to the Temperature Assessment Methodology for Use III(-P) Streams in Maryland.  Currently, an assessment methodology only exists for Class III (and III-P) streams.​

If temperature data indicates that a Use III (or Use III-P) waterbody does not meet the established temperature criteria, the waterbody is listed as impaired for temperature. Once a Class III (or III-P) water body is listed as impaired for high water temperatures, MDE prioritizes this water for Total Maximum Daily Load (TMDL) development.  MDE is currently developing the State’s first TMDLs for water temperature impairment and will provide links to additional information as it becomes available. To view a map of Maryland’s Class III and III-P streams that are impaired for high water temperatures, please view MDE’s Water Quality Assessments (IR) and TMDL Map, and click the box on the left next to the word “temperature”. ​

What is being done to protect cold water resources in Maryland?

The Department is obligated to protect cold water resources through its permitting authorities. Proper consideration of cold water resources during project development and during permitting processes can help to support Maryland’s cold water aquatic communities by preventing high influxes of warm temperature waters to vulnerable streams. The following links provide information on a variety of permitting and related activities that MDE oversees as well as guidance on BMPs, permitting, and dam removal considerations for cold water resources.

Description of MDE’s Permitting Programs and How Cold Water Protections are Implemented: Document Coming Soon

Dam and Small Pond Approval Guidelines in Coldwa​ter Resource Watersheds​​: See Small Pond Approval Process​​​​​​ webpage

How is Maryland helping to restore cold water resources?

The restoration of brook trout populations and habitat are part of the overall Chesapeake Bay restoration and climate goals. Brook trout were recognized in the Strategy for Protecting and Restoring the Chesapeake Bay Watershed, Executive Order 13508, as a key indicator species for the health of Maryland’s waters. As a cold water obligate species, the brook trout holds additional significance for the health of cold water streams. Protections for the brook trout support other vulnerable species and cold water communities, promoting the overall ecological health of Maryland’s streams. The Brook Trout Action Team was formed under the Chesapeake Bay Program in collaboration with other state agencies to facilitate cold water restoration and conservation efforts for brook trout populations. For more information on the work of the Brook Trout Action Team, click here

A specific cold water restoration effort being led by MDE is the development of Total Maximum Daily Loads (TMDLs) for water temperature in impaired Class III and III-P waters. To date, MDE has conducted spatially dense temperature monitoring in 12 watersheds around the State in preparation for TMDL development. Worth noting is that MDE’s first pilot temperature TMDL will take into account the effect of future climate change impacts. Once submitted to and approved by EPA, these TMDLs will help focus implementation efforts to those actions that best maintain and cool water temperatures.   ​

​Contact Information

For more information, please contact Melinda Cutler at melinda.cutler@​​. ​​

Cold Water Resources

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