The Three Rivers Park District in-lake phosphorus concentration goal to support direct contact recreational use for Fish Lake is 36µg/L.  The average phosphorus concentration for Fish Lake in 2007 was 50µg/L, which is higher than our goal as well as the Minnesota Pollution Control Agency impaired water criteria of 40µg/L.  The highest phosphorus concentrations in 2007 coincided with lake turnover cycles, which occur in the spring and fall of the year.  The process of lake turnover re-suspends nutrients throughout the water column and contributes to high total phosphorus concentrations near the end of April and beginning of May (75-80µg/L) and mid October (76µg/L).  Throughout the remaining portion of the year, the total phosphorus levels fluctuated ranging between 37µg/L and 62µg/L.  Although these phosphorus concentrations can potentially inhibit recreational use, the average 2007 total phosphorus concentration is lower than the 2006 average of 57µg/L.
 
The excess in-lake phosphorus concentrations were conducive for the development of algae blooms.  In 2007, the Fish Lake average chlorophyll-a concentration was 31µg/L, which is significantly higher than the water quality goal of 12µg/L.  Despite the high chlorophyll-a concentrations, the water clarity was not as significantly impaired.  The average secchi depth transparency of 1.23 m in 2007 was close to the water clarity goal of 1.4 m for recreational use. During the month of May chlorophyll-a concentrations were at their lowest, resulting in the highest secchi depth transparency of the year, which was 3m. The water clarity in Fish Lake did not begin to degrade significantly until mid July when conditions were more conducive for algae growth.  Consequently, the warmer weather conditions resulted in higher chlorophyll-a concentrations that persisted throughout the summer.  The secchi depth transparency ranged between 0.6 and 0.88 m within this time period.    
 
 
 
 
               
The Weaver Lake water quality in 2007 achieved the in-lake goals to support full contact recreational use.  In 2007, the Weaver Lake average phosphorus concentration was 36µg/L with values ranging between 27 and 72µg/L from May through September.   The concentrations were below the water quality goal of 40µg/L.  The low phosphorus concentrations resulted in significantly less algae production in 2007 with average chlorophyll-a concentration of 7µg/L.  Consequently, Weaver Lake had excellent water clarity conditions in 2007.  The average secchi depth transparency for Weaver Lake was 2.8 m.  A clear water phase that developed in May, with water clarity conditions of over 6 m, helped to increase the yearly average secchi depth.  Throughout the remainder of the season, secchi depth measurements of 1.7 to 3.0 m exceeded water quality goals.  Average secchi depth has shown a steady decrease since 2005, but compared to the past ten years, secchi measurements still remain high.
 
The Weaver Lake water quality conditions in 2007 significantly improved relative to the overall declining water quality trend that has occurred the past ten years; However, 2007 water quality declined slightly from 2006.  Several factors may have contributed to the significant improvement in water quality conditions over the past ten years.  A significant influence of Weaver Lake water quality conditions was the amount watershed nutrient loading that the lake receives.  The variation in watershed nutrient loading is mainly due to changes in the annual precipitation and in 2007, the amount of precipitation was below average for most of the summer. Then by the end of August, we approached record amounts of rainfall for the month.  In 2004, a legislative law was implemented to limit the use of phosphorus fertilizer throughout the seven county metropolitan areas to reduce potential watershed phosphorus loading.  Weaver Lake may have received less phosphorus loading from the watershed because of the ban on phosphorus fertilizer, in combination with the low precipitation.
 
A possible additional influence on the Weaver Lake water quality was the senescence of curlyleaf pondweed.  Weaver Lake has a substantial amount of curlyleaf pondweed that inhibits potential recreational use.  Consequently, a substantial amount of internal loading is due to the senescence of curlyleaf pondweed.  The released nutrients from the senescence of curlyleaf pondweed often resulted in an algae bloom that persists throughout the summer.  In 2005 through 2007, a whole lake Fluoridone herbicide treatment was completed in Weaver Lake in an attempt to control curlyleaf pondweed.  There was significantly less curlyleaf pondweed in Weaver Lake due to the herbicide treatment. The minimal increase in phosphorus concentration from 2005 to 2007 suggests that there was some curlyleaf pondweed reestablishment within the lake.  A significant decrease in the amount of curlyleaf pondweed in Weaver Lake would reduce the amount of internal nutrient loading, and subsequently improve water quality conditions.
 
These two factors may have significantly influenced the water quality conditions in Weaver Lake for 2005 through 2007.  Unfortunately, it is difficult to determine the influence that each potential factor may have had on improving water quality conditions.  Additional monitoring efforts would be necessary to determine the influence each potential factor may have had on the water quality conditions.  Consequently, it becomes critical to maintain monitoring Weaver Lake to determine potential changes in water quality conditions.
 
 
 
 
                Diamond Lake has impaired water quality conditions that inhibit recreational use.  The lake is extremely eutrophic with phosphorus concentrations consistently above 100 µg/L during the growing season.   The average phosphorus concentration in 2007 during the growing season was 154 µg/L with values ranging between 60 µg/L to 211 µg/L.   The excessive amount of phosphorus in the lake is conducive for severe algae blooms.  The average chlorophyll-a concentration was 46 µg/L in 2007.  Seasonal variation in chlorophyll-a concentrations ranged between 7 µg/L to 75 µg/L.  Consequently, water clarity conditions were extremely poor in which secchi depth measurements ranged between 0.3 to 1.19 m.  Although the water quality in Diamond Lake is extremely poor, 2007 had the best water quality overall compared to previous years, especially compared to 2006.  Average chlorophyll-a concentrations decreased from 86 µg/L in 2006 to 46 µg/L in 2007.  Secchi disk transparency increased from a yearly average of 0.34 m in 2006 to 0.56 m in 2007. The severe algae blooms provides a shading effect that inhibits the development of aquatic macrophytes.  The poor water quality conditions are partially due to large amounts of watershed nutrient loading from surrounding agricultural areas.  In addition, the shallow morphology of the lake is extremely conducive for internal loading of nutrients that are re-suspended from the sediments.  The lake is frequently vulnerable to winter and summer fish kills due to the extreme eutrophic conditions.