Every lake is different, but Michigan’s inland waters increasingly have one challenge in common: nuisance and harmful algal blooms (HABs).

In a recently recorded webinar, “HABs 101: Lake Stories,” Michigan Sea Grant and state partners invited Michiganders to share first-hand experiences with inland lake blooms and the actions they’re taking to keep their communities healthy and safe.

HABs 101: A quick primer

HABs are caused by cyanobacteria, tiny organisms that live naturally in the water. Despite being bacteria, they’re often called algae, because they get energy from the sun like plants.

Cyanobacteria thrive in warm water with lots of sunshine and nutrients. Under these conditions, they can multiply quickly enough that their population can be seen by human eyes (an “algal bloom”). Sometimes the algae produce chemicals that harm human or animal health (a “harmful algal bloom” or HAB). Even non-toxic algae can create mats, scums, or other nuisance conditions that prevent people from enjoying their pond or lake.

Michigan Sea Grant Director Silvia Newell studies the role of nutrients like nitrogen and phosphorus in freshwater ecosystems. She’s seen the effects of excess nutrients up close in lakes around the world: naturally occurring algae grow out of balance, causing problems for people and ecosystems.

She presented during “HABs 101: Lake Stories” to share background information about HABs management strategies and a case study from her own research in Ohio. “Every lake is different,” she emphasized, “[T]here are many, many factors to consider when coming up with a plan for treatment.”

A lake’s size, depth, shape, shoreline configuration, and surrounding land use all affect the way nutrients enter and exit the system. Big, warm, flat, shallow lakes with high levels of incoming nutrients are prime territory for algae blooms.

Understand your nutrient budget

For anyone experiencing algae issues on a lake or pond, the best first step is to make a nutrient budget. This step involves collecting water samples from various locations in the lake over time, under different weather conditions, and across multiple seasons to help gauge how nutrients are entering the waterbody.

Phosphorus and nitrogen loads, or increased input, often come from external sources, such as fertilizer washing off lawns and farm fields, or leaking and faulty septic systems. Nutrients can also accumulate in the lake’s sediment over time. When the water chemistry changes or the sediment is stirred up, the nutrients can re-enter the water column, providing an internal source of loading.

External loads are typically calculated with data from water samples and stream gauges, sensors that are already installed along many inland waterways and operated by the U.S. Geological Survey. Internal loads are best tested by analyzing samples of the bottom sediment in a lab.

Collecting water samples, calculating loads, and tracking patterns might seem daunting, but lake managers and residents have plenty of potential resources to tap. Read “Part 2: Let’s talk to the neighbors” for ideas.

A completed nutrient budget will help clarify the balance of external and internal nutrient sources. For lakes with algae challenges, reducing external sources of nutrients will almost always be the best and most important strategy (for more information, watch these “HABs 101: Prevention and Management” webinar clips). However, as Silvia stated, “That’s easier said than done.” Reducing some of the external sources might require significant behavioral change, money, legislation, and time.

In the meantime, lake managers and residents can start addressing internal nutrient sources. One major internal factor is seasonal stratification, which occurs during the summer when a layer of cooler, denser water is trapped at the bottom of the lake by a warmer, less dense surface layer. Without fresh oxygen from the surface cycling down into the bottom layer, organisms living at the lakebed eventually use up the available oxygen. This stratification leads to an oxygen-poor condition called anoxia, which can be fatal to aquatic life and might cause mass fish die-offs. The shift in water chemistry also triggers the sediment to release phosphorus particles that had previously been chemically bonded to iron, aluminum, or other elements in the sediment. The newly freed phosphorus can then enter the water column and feed an algae bloom.

Reducing internal nutrient loads often means keeping the water mixed and oxygen-rich, and preventing nutrient-laced sediment from kicking up into the water column. Silvia unpacked some common tactics for reducing internal loads, with the reminder that every lake is different, and tactics are best used in combination through trial and error. “These are all band-aids,” she said. “None of them are long-term solutions.”

A menu of management tactics

Under the right circumstances, algaecides, or algae-killing chemicals, can provide a short-term solution during a bloom. Copper sulfate is a common option that turns the water bright blue and effectively kills off all resident algae. However, the drawbacks are stark: killing algae cells releases any toxins the species might have already produced. The sudden die-off will deplete the lake’s oxygen supply as the dead algae decompose, potentially creating dangerous conditions for fish and other living things. Additionally, high copper levels are hazardous to humans and animals.

In addition, algae are a fundamental pillar of any aquatic habitat — destroying the bottom of the food web will eventually kill anything else living in the lake. Thus, lake managers and residents should think carefully and strategically before using algaecide to address chronic problems in a lake or pond.

Another control option is macrophyte removal — or, as many lakeshore property owners call it, “killing weeds.” However, vegetation in and around the lake can be crucial to keeping the habitat in balance. “If you have a lot of external nutrients coming into your lake, stuff is going to grow,” said Silvia, “You can basically have your choice between algae or weeds. Personally, I’d rather have the weeds, because they’re not toxic.”

Silva recommends finding ways to work with the plants, instead of against them. If lake levels dip seasonally, then plants can be cut short with special aquatic mowers or harvesters. This is better than yanking the plants up by the roots, which releases sediment, clouds the water, and creates ideal circumstances for algae to thrive. Regular mowing can be a safe, habitat-friendly way to reduce algae issues.

If extra phosphorus is mostly coming from the sediment, dredging can be effective. However, scraping off the top layer of sediment is expensive, harms the lakebed habitat, and stirs up any other settled contaminants. Dredging leaves the water cloudy, or turbid, which can give algae a competitive advantage over plants that need more light to survive. Disposing of the dredged material can also pose a challenge.

If the lake is not too deep, and internal phosphorus seems to be the main problem, aeration pumps and bubblers can help. These mechanical options mix the water enough to prevent stratification, reduce risk of anoxia, and keep phosphorus locked away in the sediment. The pumps do require regular maintenance and a reliable power source, but they can be an environmentally friendly strategy for reducing blooms.

In small or medium lakes, removing carp can be part of the solution. These bottom-feeding fish churn up sediment, making water more cloudy and less hospitable to things that aren’t algae. If external nutrient loads are already under control, removing carp can help reduce algae issues.

Finally, there are “p-binding” treatments, named for their ability to chemically bind to phosphorus ions and lock them away in a cap along the bottom of the lake. These treatments can be successful under the right circumstances. Alum (aluminum sulfate) treatments are well-established, comparatively cheaper, and effective when phosphorus levels aren’t through the roof. Phoslock is a proprietary treatment that uses lanthanum to bind up excess phosphorus. Phoslock can be more effective at holding onto phosphorus ions and works at higher phosphorus levels, but is comparatively more expensive.

P-binding treatments aren’t a sure-fire solution for all water bodies. Silvia described her experience with Grand Lake St. Mary’s in Ohio, an artificial lake with no vegetation and decades of problems with excess algae and bacterial contamination. Several failed attempts at controlling algae with p-binding treatments ultimately showed that the lake was too large, and internal and external phosphorus inputs were too high, for alum or Phoslock to effectively reduce algae levels for anything longer than a week. Watch the recording of Silvia’s talk to see how the Grand Lake St. Mary’s experiment unfolded.

Ultimately, Silvia underscored the following takeaways:

Every lake is different.
Strategies for managing algae will depend on the lake’s shape, shoreline, depth, and watershed land use.
Developing a nutrient budget will clarify the balance of external and internal nutrient sources.
In the long run, reducing external sources of nutrients is the most effective treatment for algae issues.

Check out “Part 2: Let’s talk to the neighbors” to hear from residents along Little Long Lake and Spring Lake, who are in different stages of their journeys to help keep their lakes healthy and clean.

Keep your loved ones and pets safe around a HAB

If there’s a sign about a HAB advisory or closure, follow the instructions.
Avoid wading, boating, fishing, or swimming in water with a visible bloom. When in doubt, stay out.
Keep pets from touching or drinking the water.
Blooms can grow and fade quickly and may drift around with wind and waves.
Once the water is clear, it’s generally safe to touch.

Catch up on previous HABs 101 webinar recordings to learn about fundamentals about HABs, common algae species in Michigan, and prevention and management strategies. Explore more HABS resources and see a map of past and present HABs recorded in Michigan.