Water clarity in Simcoe

Joe Mazza
Date added:
Wednesday, 13 March 2019
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Question and Answer


Hi Wil,

I seem to see reports every year of the water clarity in Simcoe turning from clear to a murkier green or brown as the winter season progresses and then clear back up again. Just wanted your thoughts on why this happens from a scientific point of view? I've read a lot of theories online including: 1. Lake turns over mid winter 2. Less photosynthesis due to snow cover and thus algae die and somehow are murking up the water 3. Nearby rivers and streams run off after a large rain.

I'm sure there is more than one factor leading to mid winter murkiness but is there a main culprit for it?

Thanks for your help!
Joe Mazza


Hi Joe,

Thanks for your question about water clarity during the winter in Lake Simcoe.  Last year the situation seemed to be heightened without the typical 'run-off from open water' explanation.  The dirty colored water was apparent to ice anglers especially at various locations around the lake. Water samples were collected but not until the situation had cleared up somewhat so no definitive answer or explanation could be found.  This year, so far, I have not heard of this occurring on a large scale like it did last winter.  I have heard that the Lake Simcoe Region Conservation Authority was going to run some water clarity tests during the course of the winter - if those dirty water conditions were present, but like I said I don't think that was the case.

Without those test results there are various hypotheses of how/why this occurs mid-winter when no run off is present ... including both of your possible explanations below. Right now though- still no certainty as to the cause.

I suspect that as soon as the creeks and rivers begin to open up and more dirty runoff water enters the lake.



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