Lake Beulah Water Quality Dashboard
HEALTH OF LAKE BEULAH: KEEP LAKE BEULAH BLUE
Current status: Blue (which is healthy and good) as of 2025
One of the values used to measure the health of a lake is the Trophic State Index (TSI). TSI is a method to numerically measure the biological productivity and health of a lake.
Over many years of surface water studies, the aquatic biology community came up with the “trophic state index,” which is a way to evaluate the environmental health of a lake or stream. Although many chemical parameters are monitored in lake water, this evaluation uses the indicator parameters of clarity (Secchi disk), phosphorus and chlorophyll-a. Because these are not co-dependent parameters, correction factors were empirically derived such that they can all be plotted on graphs with identical ranges (0 to 80), indicating the biological productivity of a water body, classified as oligotrophic, mesotrophic or eutrophic. The conditions that are indicative of oligotrophic occupies half of the scale, ranging from 0 to 40. Mesotrophic, which is the desired state, makes up only 10 points in the scale, from 40 to 50. Eutrophic values range from 50-80.
Water Quality Data from summer of 2025 shows Lake Beulah remains a Mesotrophic Lake with high-quality water. The water is moderately clear, exhibits low dissolved oxygen in deep water during the summer. The TSI values for the 2025 are phosphorus (46.9) chlorophyll-α (43.5) and Secchi value (43.8). Based on these values, all three parameters indicate that the lake is mesotrophic (moderately nutrient-rich). All three parameters are generally trending together, but there is a difference between the total phosphorus, the clarity, and the chlorophyll-a, which are more closely tracking together. This pattern is common in SE Wisconsin lakes due to the filter feeding by zebra mussels.
The Water Explorer shows that Lake Beulah is generally less clear and with higher total phosphorous and chlorophyll-a than other two-story lakes. A "two-story" lake is an ecological and angling term for a deep, cold-water lake that supports two distinct, simultaneous environments: an “upper story” near the lake surface with warm water temperatures and high dissolved oxygen levels and a deeper “lower story” with cold water temperatures and ideally high dissolved oxygen levels.
The button below will take you to the WDNR Water Quality Website for Lake Beulah. It shows up-to-date data, as well as historical data.
GRAPH OF TSI COLLECTION DATA
The following graph is from the Wisconsin DNR website. The graph shows the most recent data from 2025 at the deep hole.
Color Key:
Dark Blue (eutrophic): too many nutrients
Teal (mesotrophic): good level of nutrients
Green (oligotrophic): low nutrients/sterile
Note: TSI is not the only metric by which a lake’s health should be evaluated; it’s an indicator of the lake’s biological productivity and nutrient status. There are many ways that humans impact lake health (e.g., introduction of invasive species, warming water temperatures, excessive amounts of salt or heavy metals, damaging fish spawning habitat, loss of sensitive plant species, reducing groundwater inputs, etc.) that may not be reflected in the TSI value. There are many factors that can affect a lake’s TSI values, so it’s important to consider how these factors may have changed when evaluating what has caused a change in the TSI values.
The TSI values for the 2025 “deep hole” site are:
Chlorophyll (Green) = 43.5
Secchi (Blue) = 43.8
Total Phosphorus (Red) = 46.9
Date of Collection: 2025
Source: WI Department of Natural Resources
HOW CAN YOU KEEP LAKE BEULAH BLUE
Dos:
1. Reduce the flow of runoff into the lake, which decreases flow of pollutants and soil into the lake. Reducing the flow of runoff is especially important if your property has a steep slope to the lake.
2. Maintain your septic systems on a regular basis to avoid lake contamination.
3. Check all home cleansing products to make sure they say “phosphate free”.
4. Plant native species along the shoreline to provide habitat and food for fish and insects and prevent erosion. View this Homeowners Guide to Native Shoreline Gardens.
5. Use low phosphate, slow release nitrogen fertilizer on vegetated areas from 30-250 feet of the shoreline.
6. Travel slowly in shallow lake areas to avoid churning up the lake bottom sediments, which will decrease algae and cyanobacteria growth.
Don’ts:
1. Bathe, shampoo, or wash boats, pets, or other objects in the lake.
2. Use any fertilizer or herbicide within 30 feet of the shoreline.
3. Burn brush or leaves or dump yard clippings on the ice or water near the shoreline. They add nutrients to the water, which will increase algae growth.
4. Feed ducks or other aquatic organisms. Nutrients produced from unnatural food outside the lake’s watershed will be added to the lake through the organism’s feces.
Water Testing
Lake Beulah has been monitored by volunteers since 1991. Volunteers monitor water clarity with a black and white Secchi disk. Some also collect water samples, which are sent to the State Lab of Hygiene to be analyzed. Volunteers are the source of the majority of Wisconsin's lake water quality data, and their dedication is greatly appreciated. Additional monitoring has been done through projects funded in part by DNR Lake Grants and Aquatic Invasive Species Grants. Reports and graphs featuring data collected by volunteers, DNR staff and others can be viewed below.