Algae are a fascinating and diverse type of aquatic organism. They photosynthesize like plants, using chlorophyll pigments to create food from sunlight, but unlike plants they have no roots or leaves. Algae may be single-celled or multi-celled and often form colonies. Algae are a valuable source of oxygen and food for many species, but rapid overgrowth can harm people, animals, and the environment.
During algal blooms, colonies of algae or bacteria expand rapidly, and the overgrowth can pose a serious risk in reservoirs, lakes, ponds, and coastal areas. Harmful Algal Blooms (HAB) can threaten the health of humans and other aquatic species. Some species even release toxins that can sicken people and impact their nervous system, as well as kill fish or other animals that rely on the impacted water source.
Cyanobacteria (formerly known as blue-green algae, but technically a photosynthesizing bacteria) blooms are the most common type of HABs in lakes, ponds, and other freshwater systems across the US. It’s difficult to predict bloom events given the wide range of variables, but often bloom events are caused by nutrient pollution, like excess runoff of nitrogen fertilizers within the watershed, temperatures, or changes in precipitation that result in slow-moving or stagnant water. And these risks aren’t limited to the area where the bloom occurs, as water can travel downstream and create unsafe water conditions.
Given the scale of risks from algal blooms which is heightened by a changing climate, monitoring is essential and not always feasible with field-based monitoring alone. Lens is here to help water managers identify and respond swiftly.
The latest addition to the Lens Library is the Chlorophyll (S2), derived from Normalized Difference Chlorophyll Index. This dataset uses public sensor data to assess the concentration of chlorophyll in water bodies – a clear indicator for algae and some types of cyanobacteria on the surface of the water. The calculation uses red and red edge sensor bands from the European Space Agency Sentinel-2 constellation. Areas with high chlorophyll levels appear in bright green and yellow, and water appears blue. This index dataset may also pick up on vegetation in shallow water and <span class="term" data-def="Macrophytes are aquatic plants growing in or near water, like water lilies!">macrophytes</span>, so keep this in mind if you’re viewing along shorelines as well.
To see the new dataset in action and explore how it might be useful, head to the Lens Library to add Chlorophyll to your portfolios:
Below is an example from Lake Winnebago, the largest freshwater lake in Wisconsin. Algal blooms caused by cyanobacteria have become a yearly occurrence in this area. These blooms are due in large part to abundant nutrients, related to fertilizer use in nearby farmlands and residential lawns, among other meteorological factors. Algal blooms tend to occur in the summer months and can impede recreational activities, risk drinking water supplies, and harm aquatic life or people depending on the specific type and conditions of the bloom.
Check out the new dataset in your Lens accountor sign up today. A final note from the team: the Chlorophyll index dataset is new, and our team is interested in learning more about the current challenges and opportunities for monitoring algal blooms. If you have feedback or ideas about how the dataset may be relevant for different use cases, book a meeting with a Lens team member- we look forward to chatting!