Fish kills on Braidwood and LaSalle lakes last week drove home again the reality of recreation on the cooling lakes. It's secondary.
Cooling lakes exist to cool water used in producing electricity. Recreation, namely fishing, is a nice byproduct.
"Our philosophy, we will have good years, but we will have bad years too,'' district fisheries biologist Rob Miller said.
Fish kills on cooling lakes are generally related to low dissolved oxygen (DO) levels more than high heat, though the two are connected.
In extended hot weather, such as the last two weeks, demand for power peaks. That has increased over the years. "Look at the appliances we use,'' Miller said. More electricity is generated. The water coming out of the plants grows hotter. LaSalle's water reached the upper 90s this week.
Both fish kills were minor. On Tuesday, Region I fisheries biologist Dan Sallee surveyed LaSalle. Most affected were hybrid striped bass, with 1,439 dead.
Hybrids are more susceptible to kills than many species. But, after the last big kill, the Illinois Department of Natural Resources persuaded the lake's owner, Exelon Nuclear, to allow restocking of hybrids.
"It's been four years since we had a problem, so fishermen had four good years,'' Sallee said.
I wholeheartedly agree and hope the IDNR restocks hybrids. The feisty fighters add a welcomed dimension to our fishing world. Most fishermen understand there will be fish kills some years. It's part of a devil's deal.
On LaSalle, other species were marginally affected. Sallee said they found 20 walleye, 11 channel catfish, two sauger, three yellow bass, four blue catfish and some smallmouth.
"We had an 18-inch smallmouth jump in the boat, so there are lots of quality fish [still] out there,'' Sallee said.
Braidwood reached higher temperatures, but the problem there was most likely related to low dissolved oxygen levels.
Miller, who happened to be at Braidwood, was notified of a possible kill Tuesday. He found water temperatures at the south ramp to be 105. More worrisome were DO levels there as low as 4.6 parts per million.
The majority of the dead fish were gizzard shad and threadfin shad from 1-1/2 to 12 inches. ''They are not very thermally tolerant,'' Miller said. ''Anybody who has tried to keep them alive as bait knows they are wimpy.''
Threadfin are a recent addition to Braidwood.
"We had a big kill over there a couple years ago, and we thought we'd try threadfin shad [from Lake Springfield],'' Miller said. "The buggers took off. They were all over the place.''
Miller suspects when conditions get extreme at Braidwood, fish migrate if there is time. He found the water was in the mid-90s on the north end and DO levels a tolerable six parts per million.
However, he was concerned that "phytoplankton might have reached their limits. As those die, that takes up oxygen, too.'' Water clarity on the south end was 30 inches, a foot better than the north end. That suggests a phytoplankton die-off on the south end.
Only a few other species were observed dead by Miller: a few catfish, two carp, a few quillbacks and one bass.
In days when the cooling lakes first opened to public recreation, reaction to fish kills would be extreme. That has changed as fishermen better grasped the cyclical nature of cooling lakes.
"A lot of guys understand now this is a cost of doing business, recreation is secondary, but it is a good thing,'' Miller said. "These leases are a boon to fishermen. I think the guys saw that after 9-11 [when the cooling lakes were closed].''
Simply, fishermen need the cooling lakes in northeast Illinois.
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