Without continued work, the lake again could become a turbid body of muddy green water filled with carp and bigmouth buffalo, Robertson said.
He has been studying it since 1993, shortly after millions were sunk into the 2,000-plus-acre body of water to eliminate a rough-fish population and stop phosphorus-induced algae blooms that made enjoying the lake for recreation virtually impossible.
“If you don’t eliminate the source of the problem, the phosphorus loading, things are going to get worse,” Robertson said at a Delavan Lake Committee meeting recently.
Phosphorus, a chemical found in natural (manure) and man-made fertilizers, helps crops and lawns stay green in summer. It also promotes weed and algae growth in lakes when introduced through runoff, he said.
In the ‘70s, Delavan Lake was considered to have the second-worst lake ecology in the state, Robertson said. Phosphorus poured in from internal and external sources at more than 14,000 kilograms per year.
Since then, a slew of new practices were tried to reduce the phosphorus coming into the lake and balance the ecology to improve the fishery and water clarity.
Efforts starting in 1989 included:
-- Construction of three retention ponds in wetlands areas above stream from the Delavan Lake inlet to act as filters for water coming in from Jackson Creek in Elkhorn.
-- Construction of a large rock peninsula to try and divert water coming in from the inlet directly toward the outlet so excess nutrients wouldn’t permeate through the main lake.
-- A lake drawdown and poisoning of all fish remaining in the lake after game fish were netted out. The effort was to kill a dominant rough-fish population.
-- Game fish were restocked to create a balanced fishery devoid of rough fish.
-- Modifications at the outlet dam to keep fish from re-entering the lake.
-- Applying a chemical treatment of Alum (aluminum sulfate) to the bottom of the lake to “seal off” sediment and prevent nutrient loading from within the lake itself.
Years prior to that, Elkhorn constructed a sewage treatment plan, and the Delavan Lake Sanitary District installed a sewer system for homes near the lake, removing septic systems.
Also, best management farm techniques were promoted throughout the 27,000-acre watershed, and the town recently instituted a ban of phosphorus-based lawn fertilizers, Robertson said.
Has it worked?
Most everything that was done for the lake has shown some measure of success, but not to the levels planners had hoped, Robertson said.
The water clarity is well past the goal of 1.5 meters, but the phosphorus levels coming into the lake are above goals. The filtering ponds trapped about 30 percent of the phosphorus, less than half the anticipated amount.
It appears the Alum treatment has been covered over by new sediment, and phosphorus is again coming up from the lake bottom, Robertson said.
The lake likely would be greener if it weren’t for a balanced fishery, the most successful part of the project, Robertson said.
“We think it goes back to the bio manipulation,” he said. “That is what has kept the lake, and it’s still having an effect on the lake today.”
But even that is seeing signs of trouble with carp and bullhead being seen and caught with more regularity.
“It’s never going to get back to the way it was in the ’70s. It’s not going to get that bad,” Robertson said. But, “It could continue to degenerate. It could get bad. Carp could take over slowly. They stir up the weeds, and it could become a mess.”
Where to go from here?
“That’s hard to say,” Robertson said. “The success of this particular project depends on what you’re looking at. If you’re interested in water clarity and fish populations, we’re still in good shape and are much better than what we were hoping. The fish population, if you talk to the DNR, they’re ecstatic. (But) the algae blooms are bad.”
The town already has taken a major step by starting to dredge the retention ponds at the inlet, deepening them so they trap more nutrients and sediment. The town is planning to redesign the ponds so they become more effective, Robertson said.
The town could explore another Alum treatment, but the cost-benefit factors over time are yet unknown, Robertson said. Excessive rains in 1993 essentially washed out the initial treatment and that could happen again.
The fishery is still in good shape, and it is hoped the game-fish population will control the rough fish. That situation needs continuing monitoring, Robertson said.
Another important element to lake health is to monitor urban development and make sure it’s done right to reduce runoff from entering the lake.
“Agriculture has 10 times as many nutrients as a forest,” Robertson said. “Hands down, that’s where most of it is coming from. As (the area) gets more urbanized, it has to be done in the right way. If urban areas go up in the wrong way, it can be much, much worse than agriculture.”
The message though is clear. The project definitely isn’t over, Robertson said.
“Depending on who you talk to, this is a huge success. Maybe it won’t last forever,” he said.
1969: Delavan Lake Sanitary District created to improve lake water quality.
1979-1981: All sewage effluent diverted from lake basin.
1983: Lake experiences one of the worst algae blooms on record.
1984: Fertilizer production plant in lake watershed is shut down.
1985: Implementation of “best management practices” starts.
1989-1993: State, federal and local governments undertake a $7 million restoration project on Delavan Lake and its watershed.
----September 1989: Lake drawdown begins.
----November 1989: Fish eradication.
----1989-92: Outlet dam modified and outlet dredged.
----1990-91: Lake refilled.
----March 1990: Fish restocking begins.
----Spring 1990-spring 1992: Fishing banned.
----April 1992: Alum treatment to lake bottom.
----October 1992: Wetlands expanded and plants added.
1993: Heavy rainfall negates improvements made in nutrient reduction in lake. Over time, nutrient levels begin to increase.
1997: Aquatic plant management program begins. Town of Delavan bans the use of phosphorous fertilizers for non-agricultural use in the Delavan Lake Sanitary District.
February 2003: Town of Delavan bans the use of lawn fertilizers.
2004: Lake defined as “eutrophic”—rich in nutrients as well as plant and algal growth.
November 2006: Dredging begins at the Mound Road retention ponds.
December 2006: The city of Delavan bans the sale and use of phosphorous fertilizer for non-agricultural purposes.
“When it was first done, the lake was incredible. It has since gone down. It’s not as bad as it was in many ways. I feel like it’s kind of stable. In the last five years, it has had its ups and downs, but it has been about the same.”
“Lakefront property owners pay pretty hefty taxes, yet if the lake isn’t maintained, our property is nothing. I’d be willing to pay for improvements. If the cost-benefit ratio is good, I’m willing to kick in.”
“I don’t know that I could give you a number. Generally, I’m satisfied, but there is still distinct, marked room for improvement.”
“I suspect everybody is concerned about inhibiting any further deterioration of the lake’s water quality. There is a definite need for action on several fronts.
“I think the inlet, which (Robertson) talked about as a source of nutrients, that needs to be cleaned up. I think there is probably a real opportunity to do much, much more with the watershed and minimizing the source of these nutrients.”
“I think what everybody needs to understand is you don’t do it once and never have to worry about doing maintenance again. There will always be ongoing costs to keep water quality up.
“DLIA did a study with the UW-Whitewater about the value of a clean, healthy lake. It showed an economic impact of a clean lake is $75 million per year (to the local economy). It is more than worthwhile to pay for maintenance projects.”
“At worst, the lake could return to its pre-rehabilitation project levels. I’m optimistic there is enough support from the town and the lake residents and other governmental units to continue monitoring.
“(Robertson) showed how many agencies were involved. They’re all involved monitoring different aspects. There are plenty of people to let us know what we should be doing.”
“Primarily, ‘why did we spend all this money and why is it so bad?’ I do my best to tell them that what we’re seeing is the lake being the lake. The data shows we still have a solid lake, and we’re working on (improving) it. But we really need these people to come to meetings, be educated and stay in the loop. There is plenty we can do as users to help the lake.”
“I honestly can’t imagine anyone, after having seen the economic impact study and recognizing in today’s dollars that we will never be able to do another (full) rehabilitation project, I don’t think anybody out there would let that happen. I can’t imagine it. That doesn’t mean it will be an easy road, but I don’t picture that happening.”
“We are continuously seeing changes in the lake. Nobody knows exactly what is happening. To over-simplify what is going on in that lake will take us in the wrong direction.”
“The next thing that we really need to give attention to is the watershed. What can be done in the watershed?
“That is where most of the nutrients and phosphorus are coming from that are going into the lake.”