Sweet Briar Dam-Mid Reservoir
Morton County, North DakotaView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #3 of 4 in the county
- Public access
- Limited data
Sweet Briar Dam-Mid Reservoir in Morton County, North Dakota has a water quality grade of F (Algae-prone). Water clarity: 3 ft visibility. Phosphorus: 239.5 µg/L. Chlorophyll-a (algae): 36.9 µg/L.
- Clarity
- 3 ft
- Typical in August
- 55°F
- Type
- Hypereutrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Stays near Sweet Briar Dam-Mid Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Sweet Briar Dam-Mid Reservoir in Morton County, North Dakota — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Sweet Briar Dam-Mid Reservoir are listed below.
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Sweet Briar Dam-Mid Reservoir is a highly nutrient-loaded hypereutrophic lake in Morton County, North Dakota. Water quality is graded F based on 3 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 3 other monitored lakes in Morton County, Sweet Briar Dam-Mid Reservoir ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, NDDEQ, last sampled 2024-08-06. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The F is nutrients and algae, not a swimming clearance. Sweet Briar Dam-Mid Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 3 ft of visibility. Phosphorus 239.5 µg/L. Chlorophyll-a 36.9 µg/L. TSI 70. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 239.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 36.9 µg/L | Poor |
| Trophic State Index (TSI) | 70 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Sweet Briar Dam-Mid Reservoir typically sits around 55°F at the surface in August. Summer average is about 64°F. Usually warmest in Jun (about 74°F) and coldest in Oct (about 44°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 25 field readings (2022–2023) via the EPA Water Quality Portal. See the full Sweet Briar Dam-Mid Reservoir water temperature breakdown →
Fishing Sweet Briar Dam-Mid Reservoir
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.32 m/yr | 2 |
| Phosphorus | ↓ Declining | +62.5 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -29.3 µg/L/yr | 3 |
EPA Impairment Status
Sweet Briar Dam-Mid Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit ND-10130203-005-L_00 · Official waterbody report · Matched by proximity (0.43 km)
County Ranking
Ranked #3 of 4 lakes in Morton County
Nearby Lakes With Higher Grades
Sweet Briar Dam-Mid Reservoir holds Grade F. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Morton County
Frequently asked questions about Sweet Briar Dam-Mid Reservoir
Where is Sweet Briar Dam-Mid Reservoir?
- Sweet Briar Dam-Mid Reservoir is a lake in Morton County, North Dakota. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Sweet Briar Dam-Mid Reservoir?
- Sweet Briar Dam-Mid Reservoir in Morton County, North Dakota has a water quality grade of F (Algae-prone). Water clarity: 3 ft visibility. Phosphorus: 239.5 µg/L. Chlorophyll-a (algae): 36.9 µg/L.
Is Sweet Briar Dam-Mid Reservoir safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Sweet Briar Dam-Mid Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Sweet Briar Dam-Mid Reservoir?
- Sweet Briar Dam-Mid Reservoir typically sits around 55°F at the surface in August, from 25 EPA Water Quality Portal field readings (2022–2023). That is a typical value for the month, not a live reading.
Explore Sweet Briar Dam-Mid Reservoir across LakeQuality
Species activity outlook by water temperature and season
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Very high nutrients, dense algae, poor clarity
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Where this data comes from
45 measurements from 1 monitoring station, 2022–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North Dakota Department Of Environmental Quality
21NDHDWQ_WQX45 samples · 2022–2024
Analytical methods
- Phosphorus by Colorimetry
- 447.0 ~ EPA; Chlorophyll a and b in phytoplankton by HPLC/UV
- 4500 NO3 E ~ Nitrate in Water- Cadmium Reduction
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database