When our temperatures dip below zero, it’s hard to imagine how overall warming temperatures might be impacting our lake. Unfortunately, despite some frigid stretches, Lake Coeur d’Alene is already experiencing increases in temperature that can impact many aspects of its ecological health, including water quality and fish habitat.
As part of our monitoring efforts on Lake Coeur d’Alene, both the Coeur d’Alene Tribe and IDEQ have collected temperature data on the lake for several decades, and trends show overall the lake is warming earlier in the spring, staying warmer for longer.
This is in line with international research which has found that, globally, freshwater lakes are warming an average of 0.34° C per decade, which is faster than observed rises in air and ocean temperatures (O’Reilly, et al., 2015).
Here at home, these warmer temperatures increase the risk of toxic blue-green algae blooms, create unfavorable conditions for our native cold water fish species, and increase the occurrence and length of lake stratification, whereby temperature-influenced density layers form and reduce the mixing of oxygen into the deeper waters of the lake.
Stratification occurs in many lakes, but in Lake Coeur d’Alene, it is of special concern because of the lake’s unique history.
When there is little to no oxygen in deep waters the chemistry at the bottom of the lake may change in a way that results in sediments releasing nutrients like phosphorus into the lake’s waters.
In metals-contaminated areas, heavy metals like lead, arsenic and zinc can also be rereleased under these conditions, posing environmental and human health concerns. We are already observing strong stratification and phosphorus release from sediments in southern waters.
The number of days that our data collection site “C6” (located in Chatcolet Lake on the southern end of Lake Coeur d’Alene) has experienced anoxia, or zero dissolved oxygen, at 1 meter below the bottom has increased by 3.2 days per year since 2011.
In 2022, it experienced a record 83 days of anoxia!
In addition to warming temperatures, Lake Coeur d’Alene will be impacted by changes in timing and quantity of flows from its tributaries, including the St. Joe and Coeur d’Alene rivers and the many streams across the Basin.
Decreasing snowpack in the Basin’s high mountains, accompanied by earlier run-off events means that the waters that feed into the lake are likely to decline earlier in the year.
This can have a significant impact on both our fisheries and on recreation, decreasing river flows and even impacting summer lake levels.
So how can we protect Coeur d’Alene and ensure that its waters stay swimmable and fishable for future generations?
Just like the issue of climate change, there is no simple answer.
First, we need to urgently address the existing recommendations for protecting Our Gem’s health.
We need to reduce nutrients coming into the lake waters from various land uses (timber, development, wastewater, etc.) to mitigate the impacts of warmer temperatures that are beyond our immediate control.
Second, we must do what we can do to counter decreases in snowpack and warming temperatures by protecting and restoring riparian areas along waterways.
That shade helps keep waters cool and habitable.
Additionally, we need to adopt water conservation measures so that we are not overusing groundwater that can provide important cold-water recharge to our streams.
Finally, while our actions may not be able to locally reduce temperatures, we must play our part in reducing our greenhouse gas emissions.
We can all reduce our personal carbon emissions by reducing our home energy use, driving less, carpooling, using public transit and, when possible, purchasing low-emissions vehicles, or at least more fuel-efficient cars.
We can reduce our water use by planting drought-tolerant native plants, and watering in the cool hours of the evening and early morning.
Individuals, families, businesses and our local governments can determine their carbon footprint using tools like the one provided by EPA: https://www3.epa. gov/carbon-footprintcalculator/, and then use that information to make smart, climate-friendly decisions.
Lake Coeur d’Alene is the heart of our community, and it takes all of us to protect it for future generations.
Though climate change is a global issue, local action can make an impact on the longterm health of Our Gem, chatq’ele’, Lake Coeur d’Alene.
For more information on climate change in our state, you can check out the Idaho Climate Economic Impact Assessment, at: https:// http://www.uidaho.edu/ president/direct-reports/ mcclure-center/iceia.
