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Stormwater and Invasive Aquatic Plant Control Improves Crystal Lake
Water bod V I mDrO\/ed Cl"ystal Lake serves as a recreational resource in a highly developed
watershed. In 2002 Minnesota added the lake to the Clean
Water Act (CWA) section 303(d) list of impaired waters for exceeding eutrophication criteria. A
total maximum daily load (TMDL) study was conducted in 2011 and determined that the lake is
impaired predominantly from internal phosphorus loading sources (decaying curlyleaf pondweed
and sediment release). After implementing many best management practices (BMPs), including
harvesting of curlyleaf pondweed, stormwater outfall cleanout, stormwater pond cleanouts and
installation of a large regional stormwater system in upstream Keller Lake Park, the lake now meets
water quality standards.
Problem
Crystal Lake (19-0027) is a 292-acre lake in the
cities of Burnsville and Lakeville in Dakota County,
Minnesota. The lake is within the North Central
Hardwood Forests (NCHF) ecoregion. it is defined as a
deep lake with a mean depth of 10 feet and a maxi-
mum depth of 35 feet. The lake is a major recreational
resource for the area and is in a highly developed
watershed that spans 3,667 acres (including the lake
surface area). Several other lakes are also within the
Crystal Lake watershed, including Keller Lake (Figure
1). In 2002 Minnesota listed the lake as impaired for
exceeding eutrophication criteria (Table 1).
A summary of 1998-2008 data developed during the
TMDL showed averages of 41.8 micrograms per liter
(lig/L) total phosphorus, 24.5 |ag/L chlorophyll a and
1.7 meter Secchi disk depth for the growing season.
The TMDL called for an overall loading reduction of 31
percent and identified internal loading to be the major
source of excess phosphorus. The internal loading was
determined to be primarily from decaying curlyleaf
pondweed and sediment release.
Story Highlights
Actions that helped reduce phosphorus loading
include both in-fake management and external loading
controls by the cities of Burnsville, Lakeville, and Appie
Vailey, which are ali part of the Black Dog Watershed
Management Organization. As part of its restoration
approach, the city of Burnsviile hires a company to
conduct annual mechanical harvesting of curly leaf
Figure 1. The Crystal Lake watershed is south of Minneapolis.
Table 1. A comparison of applicable lake eutrophication
standards versus Crystal Lake datasets.
Eutrophication Water Qualitv
Standards (NCHF Ecoregion)
TP
Chi a
Secchi Depth
M-g/L
M-g/L
meters
Pre-2010: NCHF-Trophic
State Thresholds for
impairment
<45
< 18
> 1.1
Post 2010: NCHF - Aquatic
Rec. Use (Class 2B) - Deep
Lake Criteria
<40
< 14
> 1.4
Crystal Lake Datasets
Pre-2002 Crystal Lake Data
(used for original listing)
45
27.2
1.8
2006-2016 Crystal Lake Data
(used for delisting)
32.8
20.6
1.7

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pond weed across about 50 acres of the 290 acres of
Crystal Lake over a 2-week period. If not cut back, the
weed would die off in the peak of summer and release
nutrients into the water, feeding feed algae blooms.
In the mid-2000s, the city of Burnsville constructed
17 rain gardens in an existing neighborhood within
the Crystal Lake watershed as part of a paired water-
shed study (Figure 2). The study showed that the rain
gardens reduced runoff volumes by approximately 90
percent, confirming that existing residential neighbor-
hoods can be successfully retrofitted with rain gardens
and provide high levels of runoff reduction and
stormwater quality improvement.
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As part of their Phase II National Pollutant Discharge
Elimination System Stormwater permit requirements,
local cities implemented a number of stormwater
improvement projects. The cities of Burnsville and
Lakeville dredged some existing stormwater ponds
near Crystal Lake to increase their effectiveness. The
city of Apple Valley built a stormwater pond on Keller
Lake that keeps an estimated 55 pounds of phospho-
rus out of the water every year. Keller Lake was shown
to contribute 20-25 percent of the phosphorus in
Crystal Lake. To help mitigate that significant contribu-
tion, the city of Burnsville built an underground wet
vault system to treat stormwater before it discharges
into Keller Lake (Figure 3). The Keller Lake (Crystal
Beach Park) Storm Water Quality Improvement Project
received a $398,000 Clean Water Fund (CWF) grant
in 2016 from the Minnesota Board of Soil and Water
Resources. The city of Burnsville leveraged other fund-
ing in the amount of $482,000. This project reduced
the phosphorus load by 78 pounds per year (Ibs/yr),
meeting the TMDL reduction.
Figure 3. An underground stormwater treatment
system reduces contaminated water entering Keller
Lake (not visible). Crystal Lake is in the background.
Results
Review of recent data (2006-2016) indicates growing
season averages of 32.8 |_ig/L total phosphorus, 20.6
|ig/L chlorophyll a and 1.7 m Secchi disk depth (see
Table 1). With phosphorus meeting the standard and
at least one of the response variables (chlorophyll a or
Secchi disk) meeting its criteria, the lake was approved
for removal from the state's 2018 list of impaired
waters. In-iake water quality monitoring wiil continue
on this lake to evaluate trends over time and to inform
the need for modifying in-lake management. Also,
opportunities for additional stormwater treatment will
continue to be explored.
Partners and Funding
Crystal Lake cleanup projects relied on multiple play-
ers in addition to those already mentioned (Minnesota
Board of Soil and Water Resources and the cities of
Burnsville, Apple Valley and Lakeville). The Black Dog
Watershed Management Organization helped to con-
duct water quality monitoring, organize projects, and
apply for grants to benefit Crystal Lake. Other local
governmental organizations provided programs and
funding to benefit these lakes. The Dakota County Soil
and Water Conservation District offers a Landscaping
for Clean Water Grant program that makes it easy
for Dakota County residents to plan and install native
gardens, rain gardens, and native shoreline plantings.
The city of Burnsville also offers grants for residents
of up to $1,000 for projects on private property that
enhance water quality, including shoreline restora-
tions, rain gardens and native plantings.
Figure 2. A rain garden installed in the Crystal Lake
watershed in Burnsville.
0
PRO^°
s
©
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-19-001V
October 2019
For additional information contact:
Chris Zadak
Minnesota Pollution Control Agency
651-757-2837 • chris.zadak@state.mn.us

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