Date of Graduation

Spring 5-2013

Degree Name

Bachelor of Arts

Department or Program

Environmental Studies

Number of Pages



Cyanobacteria are a type of prokaryotic phytoplankton found in freshwater and marine ecosystems. Cyanobacteria often become dominant in eutrophic lakes and form algal blooms during the summer. A concern regarding cyanobacteria is that some genera are able to produce toxins, which have known adverse effects on animal and human health. The prevalence of algal blooms, specifically cyanobacterial blooms, is increasing in North America due to global warming. This thesis aims to investigate the occurrence of cyanobacterial toxins in Maine lakes and identify whether they are currently a public health concern. Microcystin-LR data was collected in 18 lakes with a history of algal blooms by the Maine Department of Environmental Protection for the Lake Assessment program in 2009. The results show that of the sampled lakes only 3 had microcystin-LR levels greater than the World Health Organization’s guideline for safe drinking water of 1.0 µg /L. This data was compared with chlorophyll a, total phosphorous, Secchi disk transparency and mean depth data collected by the Maine Volunteer Lake Monitoring Program. Chlorophyll a, total phosphorous and mean depth were not correlated with microcystin-LR. Microcystin-LR increased with decreasing Secchi disk transparency. Google Earth images were used for a qualitative assessment and discussion of land use impacts on algal blooms and toxicity levels. It is concluded from this thesis that cyanobacterial toxins are not currently an issue in Maine lakes, despite cyanobacteria being present. Regardless, it is essential to implement regular monitoring of water quality in lakes with histories of past algal blooms. Guidelines indicating at what level cyanobacteria become a concern and require intervention are suggested since cyanobacterial populations may increase in the future.