Green Headwater Lakes

Several Algonquin Park headwater lakes are characterized by a distinctive green colour.

The clear green water of Eustache Lake in Algonquin Park — Eustache Lake is purported to be the deepest lake in Algonquin Park at 90 m. This view shows the shallow north west end of the lake where it is drained by Eustache Creek. The clear greenish water that is characteristic of many Algonquin headwater lakes is very evident. The clarity is due to it being ground water fed; the greenish cast is due to the ground water's mineral content.
It is interesting to note that Keneu Lake (a much smaller lake in area) drains into Eustache Lake. Never having visited Keneu Lake, we can't comment on its colour, but the lake is protected by being within in the Eustache Lake natural zone. Wagtail lake, adjacent to Eustache Lake and at about the same elevation but draining separately into the Petawawa River, was not originally so protected (see note 1). While we have visited Wagtail Lake a couple of times, we have no memory of its colour. (However, in thinking about it, in both of the cases we were there, the lake was largely ice covered.)

Donald L Loyd, in his book Canoeing Algonquin park writes:

Ralph Bice Lake, noticeably greenish in colour, is a spring-fed headwater lake for the Petawawa River. This clear, greenish coloured water is also found in other Park headwater lakes such as Happy Isle (formerly Green lake), Whiskeyjack, North Sylvia and Whitebirch. These lakes typically have small water collection areas with relatively thin mineral soils overlying bedrock. The lake water, clear to some 7 to 8 metres in depth takes its colour from minerals leached from the soil and rock. Downstream, suspended sediments increase, toxins such as tannin build up, as do nutrients which stimulate algae. These combine to produce darker coloured water typical of most Park Lakes.

I believe this statement to be basically correct, but perhaps slightly misleading and incomplete. My interpretation is as follows:

Algonquin Park is situated on the Canadian Shield. In general, the mineral content of its soils is hard crystalline rock of very low solubility. Consequently, surface waters drain away before they have had sufficient time to pick up appreciable mineral content from the soil and bedrock. The result is that most of the water in Algonquin Park is very soft.

However, much of Algonquin Park is also poorly drained (which is characteristic of a "young" landscape. The landscape is evolving from its reshaping by the glaciers only 10 000 years ago.) This gives rise to bogs and wetlands. A bog (by definition) is a wet area that is isolated from ground water; its source of nutrients is solely rain and surface water. It is nutrient poor. The bogs are characterized by organic decay. The organic decay products, including tannins, give rise to the dark tea coloured water that characterizes Algonquin Park.

Spring Tannin Sunshine — A spring freshet displaying the more characteristic golden colour of Algonquin water.

All non-headwater lakes and streams are inevitably contaminated by tannin containing sources. The only water bodies that are not dark and tea coloured are those headwater lakes that are fed by ground water. (note the differentiation between ground water and surface water.) Ground water is able to flow through the bedrock, through the tiny crack and fissures. (Indeed finding bedrock that is not permeated by water carrying fissures is one of the challenges facing the geologic disposal of nuclear waste.) But while the ground water can flow through the bedrock, the flow rate is very low. The ground water is in contact with the bedrock for very long periods of time — in some cases thousands of years. Because the water is in intimate contact with the bedrock for such an extended period of time some dissolution of the bedrock will occur; ground water will have a higher mineral content than the surface water. Consequently, a ground water fed headwater lake where the topography is such that it is not contaminated with tannin laden surface water would be expected to have clear water with a high (or at least, higher than average) mineral concentration.

The following Algonquin Lakes are purported to be green headwater lakes: Eustache, Nadine, Happy Isle (formerly Green Lake), Loxley, North Sylvia, Opalescent, Ralph Bice, Whiskeyjack, Whitebirch.

Opalescent Lake at the Brigham Lake Portage in Algonquin Park — The Brigham Lake Portage on Opalescent Lake.
Lloyd refers in passing to "green Opalescent Lake". While I visit Opalescent Lake often, I have never consciously noticed its colour. However, this photo from my archives (2007 August) is consistent with it being a "green" lake. I'll try for a more definitive photo next season.

Now the question becomes what particular minerals (and/or mineral concentration) give rise to the characteristic green colour?

Another issue I would like to pursue is the prevalence of cedar trees adjacent to green headwater lakes. (Eastern White Cedars are often an indicator of ground water seepage because cedar trees are calciphiles. Surface water in Algonquin Park tends to be soft and acidic and thus not conducive to the growth of cedars.) There are certainly cedar trees in the vicinity of Opalescent Lake.

Notes

Sometime between 1987 and 1996, the Eustache Lake Natural Zone was expanded to include Wagtail Lake.

Sources

Donald L. Lloyd (2000); Canoeing Algonquin Park, Published by D.L. Lloyd. Distributed by Hushion House Publishing Ltd. Toronto.