A Green White Lake
In May 2018, water quality conditions at White Lake, located in Southeast NC, had deteriorated to the point where the Town of White Lake felt action was needed. Excessive nitrogen and phosphorus in the lake and warm spring temperatures had resulted in high algae levels turning its once clear waters to green. A video posted by Kyle McGee illustrates some of these conditions.
In response, the Town contracted for $500k with a company to kill algae on the lake through the use of alum (aluminum sulphate). Historically, White Lake’s waters are more acidic however it’s pH levels have been rising in recent years. The proposed treatment was to coat the lake with alum (aluminum sulphate) to kill the algae. A side effect of that treatment, however, was to raise lower the lake’s pH.
In the end, the State believes that multiple factors including the preceding algae bloom, low dissolved oxygen, and effects of the alum treatment all contributed to the kill.
How bad was the resultant fish kill? A NC Wildlife Resource Commission report on the kill estimated that 115,000 fish encompassing 9 species died, many of which are tolerant of pollution. Overall the report estimated the value of the dead fish at over $600k.
Conditions contributing to the algal bloom are ones that we need to be mindful of at all our lakes. Over development eliminating natural buffers such as wetlands, septic leachate, and over fertilization of lawns can all contribute to algae blooms. Actions to reduce threats like these will be needed from the town and the State to prevent blooms from becoming a permanent problem for lake residents.
EDIT: Fixed some incorrect wording.
This post is filled with inaccuracies.
1. Alum (aluminum sulphate) actually lowers pH when applied to a lake.
2. Elevated pH means the lake is less acidic not more acidic.
3. The pH level in white lake has been gradually creeping up over the last 30+ years as nutrient loads increase in the lake.
4. pH is usually even more elevated during algae blooms.
5. The DEQ did not say that alum raised the pH. It says that it is possible that alum could have contributed to the fish kill when fish already exposed to low oxygen and high pH levels caused an already occurring algae bloom.
6. Alum does not kill algae. It is used to permanently inactivate phosphorus, the limiting nutrient in most fresh water algae and cyanobacteria blooms. Phosphorus is bound to the alum and is no longer biologically available as a nutrient for algae and cyanobacteria.