Chlorophyll a is one of the plant pigments that is used as a measure of phytoplankton abundance--the tiny algae that are suspended in lake water.
In most shallow lakes, the relative abundance of phytoplankton is higher in the summer months, and so water clarity is lower. This is a natural cycle that is related to water temperatures: warmer water generally results in better algae growth.
Last winter, mats of filamentous algae could be seen on the bottom, and they persisted through mid-summer. This winter there has been none, but there has been a blip in chlorophyll values, which may be a result of the warm and wet conditions this winter.