North Dakota Department Environmental Quality scientists report on the quality of the surface waters in the state every other year in the even numbered years. The results of the assessment is the Section 305(b) and 303(d) listed impaired waters. For more information, please visit the NDDEQ Division of Water Quality - Watershed Management Program's website.

What is an Assessed Category stream or lake? The Clean Water Act (CWA) contains several sections which require states to report on the quality of their waters. Section 305(b) (State Water Quality Assessment Report) requires a comprehensive biennial report, and Section 303(d) requires a list of a state's water quality-limited waters needing total maximum daily loads (TMDLs) by April 1 of every even-numbered year. EPA suggests that states combine these two reports into one integrated report.

What is a TMDL? Total Maximum Daily Load (TMDL) is the amount of a particular pollutant that a particular stream, lake, estuary or other water body can "handle" without violating state water quality standards.

What's the big deal? Once a TMDL is established, responsibility for reducing pollution among both point sources (ex. pipes) and diffuse sources is assigned. Diffuse sources include, but are not limited to, run-off (urban, agricultural, forestry, etc.), leaking underground storage tanks, unconfined aquifers, septic systems, stream channel alteration and damage to a riparian area.

This dataset contains the lakes and reservoirs that have been assessed and categorized by Department of Environmental Quality-Division of Water Quality (NDDEQ-WQ) in 2022 for the 2022 integrated reporting cycle to the US EPA. The lakes are a subset and enhancement of the 1:100,000 scale National Hydrography Dataset (NHD). NDDEQ-WQ adds additional lakes or modifies outlines to reflect current conditions based on the most recent aerial imagery. Since the assessed and categorized lakes are a subset of the NHD lakes, only that subset is included in this dataset.