Changing rainfall patterns resulting from climate change are predicted to influence cyanobacterial blooms and associated production of toxins and other metabolites, but few studies have demonstrated this link. We explored seasonal and interannual trends in 2-methylisoborneol (MIB) concentrations and the correlation of these data with rainfall and hydrologic data from 2000 to 2013. We also conducted a detailed study of cyanobacterial abundances and MIB during 2 hydrologically extreme years, a prolonged drought in 2007 followed by an extremely wet year in 2008. The goal was to assess whether cyanobacterial abundances and explanatory variables that are often correlated with cyanobacterial abundances were useful predictors of MIB concentration. From 2000 to 2013, mean annual rainfall was negatively related to mean annual MIB (r = -0.50, p = 0.08) and explained 25% of the variation in MIB. In 2007, MIB and cyanobacterial abundance were high, whereas in 2008, MIB and cyanobacterial abundance were low. The total N:total P (TN:TP) mass ratio was strongly related to MIB concentration during the drought and explained 44% of the variation in MIB concentration (r = -0.66, p = 0.003). Our results suggest that rainfall and the TN:TP mass ratio may be useful predictors for MIB in drinking-water reservoirs.