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.
See Previous Reports.
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. Additionally, water samples were collected within the first two meters of the surface with a 2-meter composite sampling tube. Samples one meter above the bottom were collected with a Van Doran water sampler. Surface sample were analyzed for total phosphorus (TP), soluble reactive phosphorus (SRP), total nitrogen (TN), where the bottom samples were analyzed for TP and SRP. Surface concentrations of chlorophyll-a were also analyzed and measurements of Secchi disc depth were recorded.
| 2009 Summer Water Quality Summary |
| Parameters | Range | Mean | TSI Value | Lake Grade |
| Months | June - Sept. | May - Sept. | ||
| Secchi Depth (m) | 1.3 - 2.6 | 1.9 | 51 | C |
| Surface TP (µg/L) | 21 - 32 | 27.3 | 52 | B |
| Chlorophyll-a (µg/L) | 7 - 19 | 11.6 | 55 | B |
| Overall Score | 52 | B- |
The following summary refers to Figure 3.33 (a-d).
- Secchi disk depth increased from 2.1 m to 3.3 m by late May. From early June to late
August, secchi disk depth declined to 1.3 m. By the end of the season, Secchi disk depth
increased to 1.9 m (standard > 1.4 m). - Chlorophyll-a concentrations decreased from 9 μg/L to 4 μg/L by early May. From late
May to late September, there was a gradual increase in chlorophyll-a concentrations with
19 μg/L being the highest concentration (standard < 14 μg/L). In early October,
concentrations declined back to the standard limit. - Surface TP concentrations were below the standard limit for the entire season (< 40 μg/L)
and fluctuated between 21 μg/L and 38 μg/L. Surface SRP were below detection limit (<
0.005 μg/L) for the entire season. - Both bottom TP and SRP concentrations increased from late April to early June. In the
middle of June, both nutrients declined. From late June to late September, both nutrients
increased with the maximum TP concentration being 453μg/L and the maximum SRP
concentration being 368 μg/L. In early October, both nutrients declined. *The presence of
silica may have raised the level of SRP in the sample collected in late May (email
correspondence; RMB, 2008).
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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