Johnson Lake will reopen to swimming and paddling this summer, but Parks Canada is installing swimming docks and dumping sand on the main ‘beach’ in what it hopes will reduce the potential spread of whirling disease while the lake is open.
Crews are in the process of trying to kill off all fish in the lake (closed to angling) through electrofishing and gill nets as the first in a two-step mitigation project to keep the disease out of the Upper Cascade watershed where there are threatened westslope cutthroat trout.
The second step is to install two docks at the main beach to reduce the likelihood of swimmers touching and transporting mud from along the shoreline, where whirling disease myxospores may lie.
In addition, coarse sand will be dumped at the main beach area to make it more appealing and keep use focused in that area. A wash station will be installed in the parking lot to encourage people to voluntarily rinse off any mud from their belongings.
“We’re going to allow human use throughout summer, to let people recreate and enjoy the lake,” said Bill Hunt, resource conservation manager for Banff National Park.
“We’re trying to really knock down the number of fish now, and there will be no fishing at all, so the risk of people moving it around is limited.”
Whirling disease was detected in Johnson Lake in in August 2016 – the first case of the contagious fish disease in Canada. It’s now found throughout the Bow River watershed and several creeks and rivers both in the national park and Alberta provincial lands.
Named after the circular swimming patterns of infected fish, the parasitic disease has decimated fish populations in the United States since first being introduced from Europe in the 1950s.
Whirling disease can affect several fish species found in Alberta, including bull trout, cutthroat trout, rainbow trout, mountain whitefish, brown and brook trout. Bull trout are threatened provincially and westslope cutthroat are listed as threatened federally.
A parasite is spread through contact between fish and a freshwater worm.
Although Lake Minnewanka and the Upper Cascade watershed are currently free of whirling disease, the potential for contamination from nearby Johnson Lake remains high.
If fish living in Lake Minnewanka were to become infected, they could move into the entire Cascade River watershed and come into contact with four core westslope cutthroat populations – Sawback Lake, Sawback Creek, Cuthead Creek and Elk Lake.
Johnson Lake and the Upper Cascade River aren’t connected because of Lake Minnewanka dam, but there are still ways the disease could be transported, including by birds such as loons and osprey.
In addition, anglers, swimmers and paddlers could may transmit the disease from Johnson Lake to Lake Minnewanka and the mouth of the Cascade River with fishing equipment, recreational watercraft, even children’s toys.
Hunt said any object that comes into contact with water or mud can potentially be a vector for transmitting whirling disease from one area to another.
“We’re worried about proximity to the Upper Cascade watershed where there are westslope cutthroat, and we want to reduce the potential of the disease spreading there,” said Hunt.
Following summer, Johnson Lake will be closed after the September Labour Day holiday long weekend.
Parks will then resume electro-fishing and gill-netting to kill more fish. In mid-October, a contractor will be hired to drain the lake as low as possible, which will concentrate the remaining fish in small areas and make them easier to catch.
LIFE CYCLE
Myxobolus cerebralis, which causes whirling disease, has a complex life cycle involving two hosts: ?sh (trout or salmon species) and an intermediate host, the tiny bottom-dwelling tubifex mud worm.
Myxobolus spores (myxospores) develop in infected ?sh and are released into the environment when the fish dies. The myxospores are very persistent and can survive in moist environments for many years.
Myxospores are ingested from the environment by tubifex mud worms. The spores then rapidly multiply in the worm’s intestine.
A fragile waterborne spore stage of the parasite is released from an infected intermediate host and attaches itself to fish. This must occur within a few days for survival of the spore stage. The parasite then migrates through the fish skin into the central nervous system, and ultimately into the cartilage.
Following death and decomposition of infected fish, myxospores are released into the environment and the life cycle continues.
Spores survive passing through the digestive tract of predators, like birds, and can be transferred from place to place on muddy boots and equipment.
