Water quality monitoring in 2016 and 2017 confirmed that toxic algal blooms, bacteria, and metals are still concerns in Hicklin Lake. The lake has been monitored by King County staff since 2004, in addition to volunteer monitoring from 1996 to 1998. The lake continued to be eutrophic, with high concentrations of chlorophyll a and total phosphorus, low water clarity, and low dissolved oxygen at depth. State standards for metals were exceeded for copper, lead, and zinc.
Several projects have been completed to improve water quality in Hicklin Lake in recent years. The projects include two alum treatments in 2005 and 2011, floating wetland treatment islands, and several stormwater projects and retrofits. These projects did not resolve the water quality problems in Hicklin Lake. The study confirms the need for a comprehensive water quality investigation, which is currently underway. The Hicklin Lake Water Quality Management Assessment seeks to collect data to support the identification of site-specific actions to improve water quality.