Because of its sheltered location, Todd Lake has distinct thermal stratification levels within its water column. As a result, water below in depth remains extremely cold even during the summer. The alkalinity level is typical of other high-elevation lakes in the Cascade Range. The lake's water transparency is good, with a Secchi disk depth of . Concentration of chlorophyll in the lake is low. A 1982 study showed that Todd Lake had a high concentration of phosphorus, which is typical of mountain lakes in the central Cascades. Based on available data, the lake's trophic state is classified as oligotrophic.