A dam built in the 1950s has changed the course and temperature of a piece of the Black Ash Creek, but fisheries biologists are working on a plan to return both to their natural state.
About halfway up Blue Mountain at the Petun Conservation Area is a pond about 100 metres long on a patch of land now owned by the Nottawasaga Valley Conservation Authority (NVCA).
The pond was established by building an earth dam on Black Ash creek, which runs through the property on its way down the mountain toward Clearview Township and eventually into Collingwood and Georgian Bay.
According to Fred Dobbs, manager of stewardship services, the pond was likely built for esthetics and recreation purposes by whoever owned the property several decades ago.
He said ponds are important eco-systems, and create habitats for several different species, but in this case, the pond is damaging Black Ash Creek by warming up the water temperature and changing the way the creek flows. This is causing negative impacts on fish habitat and flood management. The dam is also a potential flooding hazard should a storm event cause it to fail completely and empty into the creek below.
Black Ash Creek is supposed to be a coldwater stream on a steep pitch – a babbling brook as Dobbs describes it. It is meant to flow over rocks like a skier over moguls.
The water in a coldwater stream is clear, and usually below 19 degrees Celsius. It’s home to the water purifier insect, the caddisfly, and is the only habitat that supports wild brook trout, which require the higher levels of oxygen found in coldwater streams. Water will flow in a coldwater stream all year because it is fed by groundwater, and not dependent on surface water.
At this site the natural path of the Black Ash Creek is through a deep valley with steep sides good for channelling floodwater when necessary.
“This is what we’re shooting for,” said Dobbs, referring to the babbling Black Ash Creek just a few metres down from the old dam.
The pond above is brown and still. It’s three metres deep, but the last metre is sediment. The two biologists at the site call it goo.
Sometimes big blooms of green algae puff up just under the surface of the pond.
In the middle, old dead tree trunks stick up through the surface of the water giving it a swampy appearance.
There are trout living in the pond, and other species making a habitat in and around it.
“Ponds are great on their own,” said Dobbs. “But attached to a river they create more surface area for the sun and wind to heat up the water … You can’t get a permit for a pond like this anymore.”
Ponds built now must be dug into the ground and cannot be fed by or empty into an above ground stream or creek.
Measurements taken by Dobbs and other NVCA staff indicate the pond can heat up the Black Ash Creek by four degrees in a day, making it inhospitable for brook trout. The wild species can hardly be seen anywhere near Black Ash Creek.
An old two-foot pipe – like construction “Big-O” – runs from the pond around the dam and into the existing creek as a way to allow water out of the pond so it doesn’t overfill. But it didn’t work.
The dam has failed partially, probably during a storm event, so water seeps over one edge and falls down the other side to rejoin Black Ash Creek. A full failure would cause flooding and damage downstream with decades-old sediment possibly reaching Georgian Bay.
So the dam will be removed by the end of September. The project is being led by the NVCA, and is sponsored by several donors, including Bruce Power, the Greenbelt Foundation, Blue Mountain Watershed Trust, Enbridge, The Georgian Triangle Anglers, and the Nottawasaga Steelheaders.
The project will cost about $200,000.
But it’s not as simple as bringing in a digger and removing the earth plug dam.
Dobbs and his fellow NVCA fisheries biologist Laura Wensink have been working on a 500-foot bypass to take water from above the dam around it and into Black Ash Creek at the bottom. The NVCA has also built a temporary dam above the pond to funnel the water into their bypass. This way, they can keep the water flowing during the work, and they won’t be sending pond water and goo down the river.
The bypass is a black tube about 10 inches in diameter with ties or stakes every foot. It has to maintain a one-degree slope and still support the weight of water flowing through it constantly.
“It looks like that because it was built by biologists, not engineers,” laughed Dobbs, pointing out the pool noodles on some of the stakes.
A contractor will come in to perform a fish rescue, removing all the fish living in the pond and relocating them to suitable areas in Black Ash Creek.
Next they’ll drain the pond and take out the sediment, which gets dried and used in area aggregate pits, which have to fill old pits with topsoil. The sediment that once grew algae in an old pond will then grow trees and grass on the former pit sites.
Crews will be digging down to the bottom of the pond in the hopes of finding the original creekbed and stones. They’ll restore the original pitch of Black Ash Creek and rejoin it with the creek below.
“This may be our largest environmental project in The Blue Mountains,”said Dobbs. “We’re going to restore a tumbling, healthy, natural stream.”
One day, with permission from the Ministry of Natural Resources, Dobbs hopes to see brook trout reintroduced to the creek at that site.
“They compliment everything else in this ecosystem,” said Dobbs. “And it would be reintroducing a heritage species.”
Though brook trout aren’t a sport fish, Black Ash Creek feeds coldwater into Georgian Bay, which is appreciated by the Rainbow Trout that spawn there.
The site is on the corner of the Collingwood, Clearview, and The Blue Mountains borders.
Having this section of Black Ash Creek return to its natural state will also provide green infrastructure to improve flood resistance during large storm events.
“We’re hoping to show leadership by example,” said Dobbs, adding he would like to see private landowners follow suit when it comes to ponds and dams on their properties that interrupt and impact streams.
The NVCA can offer support for private landowners who would like to restore the streams in the watershed to their natural state, or mitigate the negative impacts of dams in the streams.
The work to decommission the partially failed dam at the Petun Conservation Area is slated for completion by the end of September, when work on the stream has to stop due to fish spawning.
For more on the NVCA fisheries and streams programs and services, as well as landowner grants and programs, visit their website.
