Help us get serious about Phosphate in our Lake!

Quick Facts

  • over 45% of phosphates enter lakes through fertilizers
  • 40% come from animal and human waste
  • Natural decomposition and soil erosion also produce phosphates.

The Problem

  • Phosphates are perhaps the greatest threat to the ecosystem of Lake Pemichangan.
  • Phosphates encourage the exponential growth of Milfoil.
  • Phosphates act as the catalyst for outbreaks of Blue Green Algae.

The Solution

  • Stop using products that contain phosphates, especially fertilizers and cleaning products.
  • Make sure your septic system is up-to-date and well maintained.
  • Encourage the growth of shrubs and trees along on your property, especially along the shoreline.

Septic System: Diagram and Explanation

FLP’s Phosphate Abatement Program

Phosphates are perhaps the greatest threat to the ecosystem at Lake Pemichangan, from encouraging the exponential growth of Milfoil to acting as the catalyst for last summer’s outbreaks of Blue Green Algae in many lakes across Quebec. It cannot be stated enough that cottagers must cease using products with phosphates. Phosphates can be found in the following products, in order of decreasing concentrations: fertilizers, heavy duty cleaners (such as Trisodium Phosphate, a common deck cleaner), automatic dishwater detergent, common household cleaning products and naturally in human waste.

The Government of Quebec has noted the detrimental environmental effects phosphates are having on lakes in Quebec and will be implementing a program for shoreline restoration in the near future. Shoreline restoration is essential to a healthy lake ecosystem for the reasons below.

Firstly, a common fallacy cottage users have is that septic systems prevent phosphates from entering the lake—far from being true. Septic systems are not designed to absorb phosphates. Over many years of use, phosphates from human waste, cleaning products, etc. pass through the septic system and leach through the soil into the lake. (Please visit this link for a great diagram and explanation of this process.) Phosphates leach into the lake at a much faster rate when there is no vegetation between the septic system (septic field) and the lake.

Given the importance of fulsome shorelines, the Government of Quebec has decided to instate a program for shoreline restoration. Starting in 2009, free shrubs and trees will be available for cottagers to plant along their shoreline to help eliminate significant amounts of phosphates from entering lake ecosystems. The FLP Board will provide more detailed information on this newly created program this spring, so please keep an eye out for it.

Cottagers should note that the total phosphorus measurement for both lake basins (Pemichangan and Thirty-One Mile) was 8.3µg/L for 2007. This is slightly higher than last year, however results were high across the province and we are still within expected natural variation.

Phosphate Update: Fall 2007

For both basins of the lake total phosphorus was measured at 8,3µg/l. This is a bit higher than last year, but all results for 2007 seem high, and we are still within expected natural variation. There does not seem to be any trend in Pemichangan since 1997.

Prediction of Total Phosphate Concentration in the Waters of Lake Pemichangan According to the Intake of its Watershed

by Henri Fournier*
Québec Wildlife and Parks Corporation
October 2003

*translated by LPPOA/D.Dubrule/J.Fowell

REFERENCE TO BE QUOTED: Fournier, H. 2003. Prediction of the total phosphate concentration in the waters of Lake Pemichangan according to the intake of its watershed. Updated October 2003. Québec Wildlife and Parks Corporation. Outaouais Regional Directorate. Internal document. 8 p.


This document is an update of Fournier (1999). It was made necessary by a significant increase in the number of residences built along the shores of Lake Pemichangan.


The methodologies used are those described in Fournier (1999). The only adjustments were those made to the number of residences according to information provided by the Lake Pemichangan Property Owners’ Association. The number of seasonal residences is now 269 and permanent residences total 28; the development of 39 additional lots was approved but construction has not begun; finally, a project for the development of 20 to 30 properties is under discussion. All of these developments were carried out or are envisaged on the western basin of the lake.

This new information requires the following adjustments to the modelling of inputs for the western basin of the lake: the number of current seasonal residences, 269; the number of probable seasonal residences, 308; the number of possible seasonal residences, 338; the number of permanent residences, 28. There was no discussion of any conversion of seasonal residences into permanent residences. All the other modeling parameters remained unchanged.


Taking into account the new additions to the lake and following the addition of 93 seasonal residences and 19 permanent residences, one can predict that the total phosphorus concentration in the western basin of the lake Pemichangan will reach 4.5 ?g/l, an increase of 0,6 ?g/l compared to what it was in 1996. A phosphorus concentration of this nature would exceed the suggested sedentary threshold of 4.2 ?g/l (an increase of 50% of the estimated natural concentration) and would constitute an increase of 60% compared to the estimated natural concentration.

With the estimated increase of 39 residences whose development has already been approved, this would see the total phosphorus concentration in the western basin of the lake increase to more than 4.6 ?g/l; if the 30 residences whose construction is possible are added to this, the phosphorus concentration in the western basin of the Lake would reach approximately 4.8 ?g/l. Within the framework of this modelling we will assume that all these residences are seasonal. These developments would correspond to increases in the total phosphorus concentration in the western basin of Lake Pemichangan of 65% and 71% respectively, compared to the estimated natural concentration.

Given that no new inputs were indicated for the eastern basin of the Lake, the situation there remains unchanged.

We must not forget that an increase of 50% in concentration compared to the estimated natural concentration should not have a very noticeable effect on the aesthetic quality of lake water or the oxygen concentration in lake water. An increase of 100%, on the other hand, would result in the strong probability that there would be a noticeable reduction in water clarity and an oxygen deficiency in water at the bottom of the lake (Hutchinson et al.. 1991). What follows then is a decline in the aesthetic quality of the lake water and a reduction in the quality of life of the lake trout. Let us recall that Michael et al. (1996) associated a reduction in the value of the lakeshore properties to a reduction in the clarity of lake water.

The development carried out since 1996 should see an increase in the levels of phosphorus in the western basin of the Lake of roughly 15% and they should increase to almost 20% when residences are built on the lots whose development has been approved. This increase in the total phosphorus concentration could see a reduction in lake water clarity somewhere in the range of 20% which will likely be noticeable by the users of the body of water.

The western basin of the Lake seems moreover more particularly sensitive to anoxia. Our data show indeed that, in certain years, the concentration of oxygen at the bottom decreases on the side of the concentration preferred by lake trout (4 mg/l) and even on the side of tolerable minimal concentration (2 mg/l). There is, therefore, a risk that anoxia problems will develop before reaching the increased phosphorous threshold of 100% as suggested by the scientific literature. Anoxia in a large area would decrease the volume of the habitat of the lake trout, the productivity of the wildlife and the fishing interests of the Lake. Significant anoxia would involve the release of phosphorus which has accumulated in the sediment on the lake bottom. This situation does not need addressing now, but it must be considered in order to avoid an accelerated deterioration of the current situation involving the Lake.


It is urgent to control the phosphorus levels on the western basin of the lake. Already, modelling makes it possible to predict that the existing development will involve going beyond the recommended threshold. At the rate of development recorded between 1996 and 2003 the increase in the phosphorus concentration in the western basin of the lake could reach the threshold of 100% in less than 10 years. Such an increase should involve a noticeable diminution in the clarity of the lake water, a major indicator of quality, and the risk of anoxia in the water at the bottom of the lake would increase very significantly.

To these concerns one must add that of the development of periphytic vegetation on the surface of the rocks on the lake bottom, lake trout’s reproductive habitat. Our data suggest indeed that lakes with high mineral bearing water, as is Lake Pemichangan, are particularly susceptible to the development of this type of vegetation. It can reach high densities which radically reduce the survival of eggs which are deposited there, at the same time reducing the reproduction of the population of lake trout which will no longer be able to self-perpetuate.

These effects will be felt gradually with the passing of years. The change will not be constant so it will seem to be imperceptible. It is on the other hand inescapable, as evidenced by the situation of several other lakes in the Outaouais region. One can choose to wait to measure the negative effects before doing something. In this case, intervening to rehabilitate will be difficult as well as very expensive and in the worst scenario impossible.


FOURNIER, H., 1999. Prédiction de la concentration de phosphore total dans l’eau du lac Pemichangan en fonction des apports de son basin versant. Société de la faune et des parcs du Québec. Outaouais. Document interne. 19p.

HUTCHINSON, N.J., B.P.Neary and P.J.Dillon, 1991. Validation and use of Ontario’s Trophic Status Model for Establishing Lake Development Guidelines. Lake and Reserve Management 7(1):13-23

MICHAEL, H.J., K.J. Boyle and R.Bouchard. 1996. Water Quality Affects Property Prices: A Case Study of Selected Maine Lakes. Maine Agricultural and Forest Experiment Station Miscellaneous Report 398. Univ.of Maine. Orono. 16p.