2.5.1 Lakes

The Minnehaha Creek subwatershed includes the Chain of Lakes in Minneapolis and several other smaller lakes.  Powderhorn Lake in Minneapolis does not drain to the creek, but rather is pumped to the Mississippi River. 

Table 6.  Physical characteristics of lakes in the Minnehaha Creek subwatershed.

Lake 

Surface Area

Maximum Depth

Watershed to Lake Area Ratio

DNR Classification

Brownie

12

20

20:1

Natural Environment

Cedar

170

51

11:1

Recreational Development

Isles

103

31

7:1

Recreational Development

Calhoun

408

90

7:1

Recreational Development

Harriet

353

82

3:1

Recreational Development

Nokomis

204

33

4:1

Natural Environment

Hiawatha

54

30

2145:1

Natural Environment

Diamond

54

6

16:1

General Development

Powderhorn

11

20

26:1

Natural Environment

Source: Minnesota DNR.

Several of the lakes in this subwatershed are listed on the State of Minnesota's 303(d) list of Impaired Waters.  Six lakes are listed for excess nutrients, and the MCWD is preparing a Total Maximum Daily Load (TMDL) analysis for four of those lakes.  Two lakes are proposed for de-listing – Brownie and Lake of the Isles.   The TMDL will establish phosphorus load reductions and include an implementation plan that incorporates specific strategies to reduce phosphorus loading.  Six lakes are listed for fish consumption impairment by mercury.  The MPCA is preparing a region-wide TMDL for that contaminant.

Table 7.  Selected water quality goals and current conditions of lakes in the Minnehaha Creek subwatershed.

Lake 

1997 TP Goal (?g/L)

HHPLS TP Goal (?g/L)

1997-2004 Average TP (?g/L)

Water Quality Impairments

2004

TP (?g/L)

Chl-a (?g/L)

Secchi (m)

TSI

Brownie 

50

35

38

Nutrients

Mercury

45

19

1.5

58

Cedar

50

25

22

Mercury

25

7

3.7

47

Isles

50

40

40

Nutrients

Mercury

50

28

1.8

58

Calhoun

30

25

24

Mercury

15

3

5.2

40

Harriet

30

20

23

Mercury

15

3

5.2

43

Nokomis 

50

50

59

Nutrients

Mercury

PCBs

80

28

1.0

64

Hiawatha

50

50*

68

Nutrients

68

17

1.3

60

Diamond

-

90

 

Nutrients

178

38

0.8

69

Powderhorn

90

120*

 

Nutrients

118

37

0.7

68

*Hiawatha's interim goal in the draft TMDL is 61 and Powderhorn's is 90.

Source:  MCWD. 

The MCWD and partners including the MPRB, City of St. Louis Park, City of Minneapolis, and Hennepin County have undertaken numerous projects in this subwatershed to improve water quality in the lakes.  These include:

Table 8.  Previous projects to improve water quality in Minnehaha Creek subwatershed lakes.

LakeYearProjectPurpose
Brownie
  • None specific

Cedar
  • 1995-96
  • 1996-97
  • 1998
  • Twin Lakes Park Pond & Dredging
  • Cedar Meadows
  • Cedar Alum Treatment
  • Fish Screen
  • Increases storage capacity of Twin Lakes and treats water entering Twin Lake
  • Treats water entering Cedar Lake
  • Treats phosphorus in lake
  • Prevents rough fish migration from Cedar Lake to Cedar Meadows
Isles
  • 2004-present
  • MPRB Isles Renovation Plan
  • Shoreline stabilization, native plant restoration, wetland enhancement and restoration

Calhoun
  • 1999
  • Lake Calhoun Ponds
  • Three cell wet detention system to treat stormwater prior to entering Lake Calhoun
  • Alum treatment
Harriet
  • 1994-present
  • MPRB/Minneapolis BMPs
  • Increased street sweeping, additional grit chambers (1994-96), constructed wetlands (1998), and littoral alum treatment (2001)
Nokomis
  • 2001
  • Lake Nokomis Improvements
  • Three ponds to treat runoff, additional grit chambers, an inflatable weir at the outlet, rough fish removal
Hiawatha 
  • None specific
 
Diamond
  • 2000
  • 60th Street & 1st Avenue Pond
  • Alleviates flooding and treats stormwater discharging to Diamond Lake
Powderhorn
  • 2001-present
  • MPRB/City Restoration Plan
  • Five continuous deflective separation grit chambers (2001), native plantings (2002), alum treatment (2003)