When lakes start to fail the usual suspects for decline are increased phosphorous and nitrogen — normally due to increased development. What has puzzled scientists studying Square Lake is that there has been no increase in these chemicals. Yet, water clarity continues to worsen.
So, what’s happening?
One reason for good water quality in Square Lake was a thriving population of tiny, algae-eating zooplankton called daphnia pulacaria. Unfortunately for them, Daphnia are also the favorite food of trout. In the 1970 through the 1980’s the DNR began to stock non-native rainbow trout in Square Lake because trout thrive — but do not reproduce — in the clear, cold waters of the lake. Twice a year, for the benefit of a small group of trout anglers, the DNR stocks Square Lake with thousands of trout that primarily feed and grow on daphnia.
Not surprisingly — and as with most human manipulation of nature — things began to go wrong. Long-term water monitoring studies showed an alarming, steady downward trend in water clarity. For example, the 22 feet average water clarity seen in 2000 has fallen to 14.75 feet this year. Scuba divers have now packed up and moved to cleaner lakes.
The warning bells were sounded in the late 1990s when the trend toward decline started to emerge. However, despite having no scientific evidence that trout stocking was good for the lake, the DNR was reluctant to change. The DNR made it clear that the evidence and burden of proof was on those questioning DNR policy.
That evidence is now before us. After years of thorough study, recent Clean Water Partnership research concluded, “that trout predation on the algae-eating daphnia is the likely cause for the lakes decline in water quality.” Scientists, consultants and the Carnelian-Marine on St. Croix Watershed District are now calling for a three-year moratorium on DNR trout stocking.
You’d think these compelling facts would persuade the DNR to abandon stocking completely. But no, the DNR’s response to this research was to conduct a public hearing last week to consider liberalizing regulations and allow trout anglers to catch more fish. The new DNR theory is by allowing anglers to catch more trout there would then be more daphnia eating algae. In short, trout stocking would continue. The attending trout anglers thought this was pretty good idea and no wonder. The last creel survey showed anglers only caught around 300 trout. Again, there is a troubling absence of any DNR scientific fact or evidence to support this theory.
I would hope that wiser heads would prevail before we ignore science and gamble away the health of a declining lake by betting on a risky DNR policy of best guesses. After all, that’s what got us here in the first place.
But all is not lost. For the first time the DNR fisheries personnel appeared to understand the trout-daphnia-algae connection and listened to the informed, reasoned testimony of scientists and knowledgeable watershed leaders. Faced with mounting evidence, the DNR announced a move in the right direction by agreeing to a one-time, temporary stocking cessation this fall. Public comment for the trout regulations and moratorium ends on Sunday. There is now hope the DNR may do the right thing.
This controversy raises serious questions about unintended consequences, bureaucratic intransigency and how public policy is shaped. But more to the point, for whom are we managing our lakes? Square Lake should not simply be fish tank managed for the benefit of a handful of trout anglers catching only a few hundred fish. The benefits are small and the results have been disastrous. Ignored or forgotten in all this are the thousands of beach goers, boaters, swimmers, and scuba divers who simply want to enjoy what were once the cool, cleaner waters of Square Lake.
Dean Ireton Tharp is president of the Square Lake Association.