North Arm (DNR ID: 27-0133-13)
Sampling Location GPS Coordinates: Surface Area: 307 acres Max. Depth: 64 ft
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North Arm is located near the cities of Spring Park and Orono. Head east on Minnetonka Blvd, and turn left on Co Rd 101 S. Turn right at Grays Bay Blvd and continue on Bushaway Rd. Turn left on Eastman Ln/Shady Ln, then a slight right at E Circle Dr. Next take a slight left at Lake St. E. Turn left at Ferndale Rd S and continue on Shoreline Dr. Turn right at Northshore Dr. Public lake access is available at the North Arm boat access.
North Arm is on Lake Minnetonka which is a class 2B lake protected for aquatic life and recreation. Water quality information is available beginning in 1997. MCWD staff have been monitoring the site on North Arm on a bi-weekly basis from the time of ice out (April) to the time of fall mixing (mid-October) since 2006.
Currently not available.
Monitoring season started in late April and ended in late October. A YSI multi-probe sonde was used to measure dissolved oxygen (DO), temperature (oC), pH, and specific conductivity (µS/cm) at each meter depth from the water surface to the bottom. Water samples were collected at one meter below the water surface and one meter from the bottom. Surface and bottom sample parameters analyzed included total phosphorus (TP), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP), total nitrogen (TN), total dissolved nitrogen (TDN), nitrate/nitrite (NO3/NO2) and ammonia (NH4). Surface concentrations of chlorophyll-a were also analyzed and measurements of secchi disc depth were recorded.
| 2008 Summer Water Quality Summary |
| Parameters | Range | Mean | TSI Value | Lake Grade |
| Months | June - Sept. | May - Sept. | ||
| Secchi Depth (m) | 1.3 - 4.0 | 2.3 | 48 | B |
| Surface TP (µg/L) | 23 - 32 | 27.6 | 52 | B |
| Chlorophyll-a (µg/L) | 5 - 24 | 11.8 | 55 | B |
| Overall Score | 52 | B |
The following summary refers to Figure 3.33 (a-d).
- Secchi disk depth decreased slightly in the beginning of the season then increased from 1.3 m to 4 m by early June (standard > 1.2 m). Secchi disk depth decreased for the remainder of the season with a small increase in late August and October.
- Chlorophyll-a concentrations were greater than 10 µg/L for majority of the season with the maximum concentration reached in early August at 24 µg/L. From June to late July, concentrations ranged between 4 µg/L and 8 µg/L (standard < 15 µg/L).
- Surface TP concentrations were below the standard limit for the entire season (< 40 µg/L) and fluctuated between 21 µg/L and 39 µg/L. Surface SRP were below detection limit (< 0.005 µg/L) except in late May, and early July*. *Early July surface and bottom samples may have been mislabeled which may explain the change in both SRP concentrations.
- Both bottom TP and SRP concentrations increased from late April to October. Bottom TP concentration was the maximum at 438 µg/L, where bottom SRP concentration was the maximum at 352 µg/L. SRP concentrations declined from 49 to below detection limit (< 0.005 µg/L) from the late June to early July, see above for further explanation*.
Lake Grades and Historical Monitoring Summaries
When available, previous reports are linked to applicable year. Additional lake data previous to 2007 may be available in the applicable year's hydrodata report. If you have additional questions or you are looking for specific information please contact MCWD's Water Quality Staff.
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