Bone Lake, or Onondogacona as it was named by its Native American inhabitants in 900 AD, is a 1,667 acre lake located in Polk County. It received its unorthodox name after early European inhabitants found the remnants, and bones, of Native Americans on an island in the lake. Originally named Lake of the Small Pines in the Ojibwe language, this scenic lake supported a trading post at its south end during the early 1700s.
Today, the large lake supports more than 500 residential lots along its 12 mile shoreline. Over the years, the large lake population has weighed on the lake’s water quality along with changes in the lake’s watershed. Since 1995, DNR has provided 18 grants to the Bone Lake Management District that address water quality, aquatic plant management and aquatic invasive species prevention and control. For example, a 2008 Lake Management Planning grant helped develop five goals the District is working to accomplish. These included:
- Improving Bone Lake’s water quality by 20 percent in 10 years;
- Maintaining and enhancing Bone Lake’s natural beauty;
- Protecting and enhancing the wildlife habitat;
- Protecting and improving Bone Lake’s fishery; and
- Maintaining safe, effective navigation on Bone Lake.
Since then, the lake has received additional grants from the DNR to implement the lake management plan, create a comprehensive aquatic invasive species detection and response plan and develop an aquatic plant management plan.
Outreach efforts supported by DNR included the production on an educational map of Bone Lake that was mailed to all property owners. One long time, permanent resident remarked, “I had no idea there was so much wildlife here.”
More than 45 percent of runoff into Bone Lake comes from residential areas around the lake and contributes to water quality problems. The runoff contains phosphorus which fertilizes algal growth. As a result, the Bone Lake Management District has offered its residents free environmental consultation visits, native plant reimbursement plans and help with replacing septic systems. The native plantings stabilize soil and capture runoff while new septic systems replace old ones that leaked phosphorus and other nutrients.
In 2006, the average water clarity reading on a secchi disk reading was only five feet. In 2014, six years after implementing their lake management plan, the secchi disk reading increased by 70 percent to 8 ½ feet, which is the average secchi disk depth of nearby lakes.
Though the District’s efforts seem to have improved water clarity, Bone Lake continues to fluctuate between mesotrophic and eutrophic on the trophic state index. The trophic state index is a composite measure of phosphorous, chlorophyll and secchi disk readings and indicates lake water quality during the summer months.
One result of low oxygen levels in the deepest parts of the lake is internal loading. Internal loading occurs when phosphorus bound to iron in lake sediments is liberated into the water column. With adequate oxygen levels phosphorus remains bound to iron. When oxygen becomes scarce iron changes chemically and releases the phosphorus it previously held. Back in the water column, phosphorus can again stimulate algal growth. A DNR funded study of Bone Lake showed that internal loading was a significant contributor to the lake’s phosphorous load (23 percent).
While the hard work of DNR and the Bone Lake Management District have shown improvements in water clarity, opportunities for additional advances remain. Current studies funded by DNR grants are working to determine the best steps to implement the Bone Lake’s management plant. With continued efforts, the water quality of Bone Lake will get even better. The decades of effort by residents of Bone Lake demonstrate the important role they play in the lake’s health and well-being.