2.5.1 Lakes

Dutch Lake is the primary receiving water within the subwatershed.  Water quality in Dutch Lake has since 2000 consistently been scored in the C-D grade range on the District’s annual lake report cards.  The mean summer 2004 total phosphorus concentration was 88 ?g/L, well in excess of the District’s 40 ?g/L goal and the highest average concentration since 1997.  It also exceeds the standards being developed by the State of Minnesota and is in an impaired use condition, although it has not been formally designated an Impaired Water.  Dutch Lake is a Metropolitan Council Priority Lake.  The Council uses the priority lake list to focus its resources as well as to determine which lakes need to have a nutrient budget analysis completed as part of environmental reviews when they are impacted by a proposed project.

Table 4.  Physical characteristics of lakes in the Dutch Lake subwatershed.

Lake 

Surface Area

Maximum Depth

Watershed to Lake Area Ratio

DNR Classification

Dutch

160

45

10:1

Recreational Development

Source: Minnesota DNR

Table 5.  Selected water quality goals and current conditions of lakes in the Dutch Lake subwatershed.

Lake

1997 TP Goal

HHPLS TP Goal

1997-2004 Average TP

2004

TP (?g/L)

Chl-a (?g/L)

Secchi (m)

TSI

Dutch

50

40

67

88

44

1.1

65

Source: MCWD

According to standards established by the MPCA, water quality in Dutch Lake is not supportive of swimming.  Modeling performed for the HHPLS and for preparation of this plan indicates that phosphorus loading from runoff in the watershed cannot explain the total phosphorus concentrations in the lake.  Internal loading from lake sediments or phosphorus exported from the extensive wetlands that drain to the lake is likely a root cause of the higher than expected in-lake TP concentrations and excessive late spring algal blooms.