Across the world, reported numbers of toxin-producing harmful algal blooms (HABs) in freshwater bodies have spiked. Oregon does not escape this fate. Lake Billy Chinook has seen HABs each of the last five summers – an alarming development. These HABs threaten water quality, strain local economies, and affect the health of people, fish and wildlife, and whole ecosystems. Though many point to climate change as the spike’s main cause, that explanation fails to look at the whole picture. A better explanation for the spike is human activities, especially those that pollute water, impair water quality, and provide optimal conditions for HABs to flourish in. At Lake Billy Chinook, the major contributors are nutrient pollution from agricultural runoff, the loss of riparian habitat along its tributaries, and impounded, stagnant waters. Looking at all of these additional pressures, the increasing frequency of HABs at Lake Billy Chinook is a foreseeable outcome.
How do HABs form in the first place?
Algae flourish in warm, sunny, stagnant waters with high nutrient contents. Warm and stagnant waters allow algae to occupy the surface of the water without being disturbed and sunlight allows photosynthesis and growth. Unnatural infusions of nutrients give algae the building blocks they need to continue to grow in dense concentrations. These conditions readily result in large HABs.
Nutrient polluted freshwater systems impair water quality to algae’s benefit. Some of the largest contributors to HAB-causing water quality impairment are nutrient pollution from agricultural runoff and forestry practices, removing riparian habitat which filters runoff and provides shade, and increasing temperature through water withdrawals and stagnation. The HABs resulting from these activities point to a larger issue – freshwater systems are overtaxed by nutrient and temperature pollution and can no longer function properly.
Climate change is responsible for some water warming and providing favorable weather conditions for algae. However, if climate change was the main contributor, similarly situated freshwater bodies would experience HABs at similar rate – which they are not. Human activities that pollute and impair water quality provide a better explanation for this difference in HAB occurrence rates.
Why is Lake Billy Chinook seeing so many HABs?
Lake Billy Chinook is at the forefront of the HAB spike in Oregon. It owes this dubious distinction to the excellent conditions it provides for algae to thrive in. Nutrient pollution is high, surface water temperatures are above healthy levels, and the water is largely stagnant. With these conditions, the significant uptick of HABs at Lake Billy Chinook is not too surprising.
But how did conditions at Lake Billy Chinook get this way? Human activities throughout the Deschutes Basin are the main contributor. Agricultural runoff transported by the Crooked and middle Deschutes rivers, lost filtration and shade once provided by riparian vegetation along the tributaries, water withdrawals, and impoundment operations all impair Lake Billy Chinook’s water quality and offer optimal conditions for HABs.
The water quality situation at Lake Billy Chinook is unique in that it is largely at the mercy of its three tributary rivers for its own water quality – the Metolius, Deschutes, and Crooked rivers. Lake Billy Chinook’s nutrient pollution problem comes largely from one source – the Crooked River. Runoff from both animal feed operations and farms, which use 25% more fertilizer compared to 55 years ago, enter directly into the Crooked River. That runoff is no longer filtered by riparian vegetation. The Crooked River’s nutrient infusions, which account for 86% of Lake Billy Chinook’s dissolved nitrates, feed algae and potential blooms.
Lake Billy Chinook’s high temperature comes from many sources. Climate change, however, is not a major contributor. Over the last 20 years, surface water temperatures at Lake Billy Chinook have not increased much. On the other hand, many temperature-raising factors have stayed constant during that same period. Both the Deschutes and Crooked rivers’ temperatures are, and have been, well above the protective criteria level set by the State for the Deschutes Basin. Water withdrawals continue to reduce the amount of water in the Deschutes and Crooked rivers, allowing them to warm more quickly. Finally, impounding water both increases the exposure time of water to more solar radiation, which increases water temperature and stimulates algal growth. These conditions have persisted during the last 20 years and explain Lake Billy Chinook’s high temperatures better than climate change.
Freshwater bodies are in a constant, delicate balance with countless factors contributing to their health and status. Lake Billy Chinook provides a clear example of how the human activities are the major contributing factor to the HAB spike, both locally and worldwide. Climate change alone cannot explain this spike. Nutrient pollution and temperature-increasing human activities provide a clearer explanation. Lake Billy Chinook’s current water quality conditions provide a nutrient-rich, warm, and stable environment for algae to thrive year after year. If these conditions continue, HABs will continue to occur in Lake Billy Chinook.