Phosphorus is a naturally occurring nutrient and a main driver of algae growth. One pound of phosphorus can produce up to 500 pounds of algae. Increased algae levels create low oxygen and poor light penetration in lakes, reducing quality of fish and wildlife habitat.

High phosphorus levels determine whether the water looks like pea soup or an aquarium. Excessive algae can produce foul smells and toxins harmful to humans and pets. To prevent this, it’s important to keep sediment and nutrients on the landscape and out of waterbodies.

Chlorophyll-a measurements are used as an indicator of photosynthetic activity and algal biomass. Waters with high levels of nutrients from fertilizers, septic systems, improper sewage treatment, and urban runoff may have high concentrations of chlorophyll-a and excess amounts of algae. Chlorophyll-a works together with phosphorus to drive algae growth. Staff observe the relationship between the two when reviewing the data. 

Algae adds oxygen to the water as a by-product of photosynthesis, but too much algae can contribute to decreased levels of dissolved oxygen, which is needed for aquatic life. Excessive algae increases the risk of undesired odors and blue-green algae blooms, which can be toxic.

A Secchi disk is a flat metal disk that is lowered into the water until it can no longer be seen. The depth where the disk disappears, called the Secchi depth, is a measure of the transparency of the water.

Poor transparency means there’s extra nutrients, algae, sediment, or other debris in the water. Transparency is the most basic indicator to assess risks for most lake uses, and informs us of potential issues that could occur further downstream. Transparency can be influenced by pollutants or sediment draining into the lake from the surrounding land area or by existing sediments recirculating from the lake bottom.

Chloride is a common ingredient in salt de-icers and home water softening. Chloride is a permanent pollutant to water quality, and it takes only one teaspoon of salt to pollute five gallons of water. It is toxic to aquatic life and interrupts lake temperature and nutrient cycles.

Chloride poses threats to freshwater and even drinking water supplies. There is no economical way to remove it. VLAWMO currently has no waterbodies impaired for chloride, but some lakes show upward trends. Lake chloride levels can decline as water flushes through, but the chloride will carry through to rivers, other lakes, or groundwater.

The Trophic State Index (TSI) is a classification for lakes according to their nutrient levels. Different classifications pertain to the amount of productivity occurring in the water. While nutrients are naturally occurring and needed in the aquatic ecosystem, excess nutrients are a form of water pollution that create imbalances and impairments in the aquatic ecosystem. Water resource managers use an equation using phosphorus, Secchi disk, and Chlorophyll-a data to create a TSI rating. 

• Lakes with lower TSI ratings (below 30) are generally low productivity, clear, and best for water sports.
• Lakes with medium TSI ratings are generally support a range of aquatic habitat including fish, plants, algae, insects, and other wildlife.
• Lakes with a high TSI (above 71) are considered to be high in biological productivity and likely have an excess of nutrients. This can create a range of conditions including an algae-dominated, turbid water state. 

Over half of Minnesota's waterbodies are listed as impaired by the Minnesota Pollution Control Agency (MPCA). Many of these are impaired for high nutrient levels, and the VLAWMO watershed has several lakes listed with this status. 

Conductivity: Conductivity is a measure of water's ability to pass an electrical current. A high conductivity indicates dissolved salts or other inorganic chemicals that conduct electrical current. Water resource managers keep track of a conductivity baseline for each waterbody to allow for a comparison if significant changes occur. 

Temperature: Water temperature can impact which kinds of organisms live in waterbodies. The rate of chemical reactions generally increases at higher temperatures, as warmer water holds less dissolved oxygen, which is needed for aquatic life. Impervious surfaces such as parking lots can contribute to hotter lakes and wetlands, such as stormwater runoff hitting hot pavement on a summery day. This runoff enters lakes, streams, or wetlands warmer than if it went through soil or green infrastructure such as a raingarden. 

Nitrogen: Excess nitrogen can cause an overstimulation of growth in algae or aquatic plants. High nitrogen levels can pose risks for nitrate contamination in shallow groundwater. 

pH: pH is a measure of how acidic or basic the water is. It tells us how nutrients or metals can be dissolved in a given waterbody, and what the waterbody can make available (i.e. phosphorus) for aquatic life. Water resource managers keep track of pH baselines and look for sudden changes that could provide clues to other issues. 

Macroinvertebrates: Macroinvertebrates are organisms that lack a backbone and are large enough to be seen with the naked eye. Examples include dragonfly and mayfly nymphs, crayfish, scuds, clams, snails, and aquatic worms. Different species of macroinvertebrates have different sensitivities to pollution or imbalances in the aquatic ecosystem. Water resource managers look to macroinvertebrates for hints at short and long-term trends in the aquatic environment, and to compliment chemistry data.