Among the many natural phenomena that grace the Northwoods, one of the most intriguing is the annual event known as “lake turnover.”

What is Lake Turnover?

Lake turnover, often referred to as lake mixing, is a vital process that occurs in temperate and polar regions, including the lakes of Forest County. This natural phenomenon takes place when lakes undergo a seasonal shift in water temperature and circulation. There are two main types of lake turnover: spring turnover and fall turnover.

Spring Turnover occurs as winter gives way to spring. During winter, the surface of the lake becomes colder than the deeper layers. As the air temperature rises and the ice melts, the warmer surface water starts to mix with the colder water below. This mixing is driven by changes in water density due to temperature and, in some cases, wind. As the lake turns over, it becomes fully mixed, allowing nutrients and oxygen to be evenly distributed throughout the water column. This is a crucial event for the health of the lake’s ecosystem.

Fall Turnover, on the other hand, occurs when the weather cools down in autumn. As the surface water cools and becomes denser than the water below, it sinks, initiating a similar mixing process. Fall turnover is essential for replenishing oxygen in the lower layers of the lake and ensuring that nutrients are brought up to the surface where they can support aquatic life.

Why Does Lake Turnover Matter?

Lake turnover plays a pivotal role in maintaining the health and balance of Forest County’s aquatic ecosystems. Here’s why it matters:

  1. Oxygen Distribution: Lake turnover ensures that oxygen is distributed evenly throughout the water column. This is vital for the survival of fish, insects, and other aquatic organisms that rely on oxygen for respiration.
  2. Nutrient Cycling: During turnover, nutrients, such as phosphorus and nitrogen, are mixed from the lake bottom to the surface. This process supports the growth of algae and phytoplankton, which are the base of the aquatic food web.
  3. Temperature Regulation: Turnover helps regulate the temperature of the lake, preventing extreme temperature fluctuations that could harm aquatic life.
  4. Fish Habitat: Many fish species in Forest County lakes rely on specific temperature ranges for spawning and feeding. Turnover ensures that these temperature gradients are maintained, providing suitable habitats for different fish species.

Impacts on Forest County’s Ecosystems

The annual cycle of lake turnover has far-reaching effects on Forest County’s ecosystems. Some of the notable impacts are:

  1. Biodiversity: Lake turnover promotes the growth of algae and phytoplankton, which serve as the primary food source for a wide range of aquatic life. This abundance of food supports a diverse community of fish, insects, and other species.
  2. Recreation: Turnover can affect recreational activities such as fishing. Anglers often target certain fish species during specific seasons when turnover creates optimal conditions for their catch.
  3. Water Quality: By redistributing nutrients and oxygen, turnover helps maintain water quality. Properly mixed lakes are less susceptible to issues like harmful algal blooms.

Conservation and Management

Understanding and managing lake turnover is crucial for the long-term conservation of Forest County’s lakes. Conservation efforts should focus on:

  1. Monitoring: Regular monitoring of water quality, temperature, and nutrient levels can help identify changes in lake conditions and potential issues.
  2. Educational Initiatives: Promoting awareness about the importance of lake turnover and responsible lake use among residents and visitors can help protect these valuable resources.
  3. Preservation: Protecting the surrounding forests and wetlands is essential, as they play a role in regulating water quality and providing habitat for wildlife.

Lake turnover is a fascinating natural process that shapes the ecosystems of Forest County. Its impact on water quality, biodiversity, and recreational opportunities cannot be understated. By understanding and respecting this annual event, we can contribute to the conservation and sustainable management of Forest County’s beautiful lakes for generations to come.

Conservation Corner is a weekly article produced by the Forest County Land & Water Conservation Department. For more information contact Steve Kircher, County Conservationist-Land Information/GIS Director at 715-478-1387 or by e-mail at .