For the past four or five decades, Minnesotans have invested an enormous sum of money aimed at protecting and improving lake quality. More recently, we have amended our constitution to tax ourselves to invest $100 million per year for 25 years to further improve water quality. So, where do we stand?
We are fortunate that the University of Minnesota established a citizens’ lake monitoring program in the early 1970s (now administered by the Minnesota Pollution Control Agency, MPCA). This program has provided a long-term record from which to evaluate trends in lake quality, specifically water clarity.
Minnesota’s lake water quality efforts are focused in large part on recreational “impairments” as measured by phosphorus content in lake water. Both measures, phosphorus and water clarity, are highly correlated, so it’s instructive to look at these as a measure of how we are doing.
To evaluate trends for this article, I reviewed the MPCA’s Water Quality Assessment and Impairment database for lakes greater than 20 acres within the Minnehaha Creek Watershed. This database includes monitoring data from the early-1970s to present in many cases. Data from other metro watersheds show similar results.
Here is what I found for watershed lakes, excluding Minnetonka: Only 22 (of 38) had sufficient data for evaluation. Of those with sufficient data, 91% of lakes show no trend in water clarity, and one lake improved and one degraded.
What does this mean?
Despite intensive watershed management activities spanning at least four decades, there have been no substantial improvements in water quality. But it also means that whatever we are doing in the watershed that could be degrading lake quality is also not having a negative impact.
This is not what we have been taught. How can this be?
Evidence from lake sediment studies demonstrates that our lakes degraded following European settlement, specifically there was a significant increase in lake phosphorus between the late-1800s and now. Yet, data from the past half century indicates no changes. Profound landscape alterations occurred following European settlement, which led to substantial and irreversible changes to lake watersheds at that time. However, subsequent modifications to lands tributary to lakes have been small in comparison – the damage to lakes occurred long ago.
Most lakes (71% in this watershed) are now impaired, meaning they have more phosphorus than the state standard, and this impairment occurred long ago. Excess phosphorus causes nuisance algae blooms and poor water clarity.
So, despite our efforts and investments, many of our lakes are impaired, but not getting worse, and almost none of our lakes are improving. It is unclear whether our investments in lake protection are holding the line on lake quality. Really though, we desire improved lake quality and for the most part we are not seeing that.
What should be done?
If we are making large investments, we should expect results. Since the enactment of the Clean Water Act, the only lakes in the country that have improved were those where sewage inputs were mitigated, which has been substantially controlled since the 1980s. Since then, we have shifted our regulatory and management attention to watershed pollution. There are practically no cases in the United States where impaired lakes have improved as a result of watershed best management practices – such as ponding, rain gardens, buffer strips, etc.
Watershed management as a method to improve lake condition (in terms of phosphorus impacts) requires a complete and profound re-engineering of the watershed’s hydrology. In the case of the Yahara Lake chain (Madison, WI) – Lakes Mendota, Monona, Waubesa, and Kegonsa – it has been estimated by the Clean Lakes Alliance it will require an expenditure of over $600 million dollars and 20 years to get half way to their goal.
Many lakes around Orlando, FL have improved following the construction of near-shore treatment facilities that intercept inflows and treat them. The price tag (per lake) is in the tens of millions of dollars plus operational costs. Good lake quality is important and they expect, and get, results.
There are ways to fix impaired lakes. For example, Green Lake (Seattle WA) has maintained significantly improved water quality with periodic alum treatments since 1991, recognizing that decreases in runoff phosphorus inputs are impractical.
I think it’s time to step back and evaluate what we want to accomplish for our lakes and how to best get there. We have a credible, long-term record that tells an important story. We should pay attention to it.