Press Release

BALTIMORE, MD (April 19, 2002) – The Emergency Response Division of the Maryland Department of the Environment (MDE) and other emergency responders around the region have been receiving numerous calls about what appears to be yellow-green paint or a similar substance in parts of Maryland waters – especially along water edges – and in puddles. In all instances so far investigated, the substance has been accumulations of tree pollen.

Due to the recent heat wave and the region’s predominantly dry weather, the entire Chesapeake Bay region has been experiencing extremely high tree pollen accumulation and pollen counts in the air at over 1,000 particles per square meter on April 18 (

Currently, the predominant pollen sources are maple, cedar/juniper, sweet gum and oak trees. During periods of heavy tree pollination a fine green film of minute pollen particles is visible on cars, parking lots and other surfaces. Typically these particles are flushed into the nearest waterway with rainwater and can accumulate in stagnant water, along edges of waterways and around the fringe of puddles. Yesterday’s storm, which may have helped reduce pollen in the air, has washed additional pollen into the water.

At times, these pollen concentrations can become dense enough to appear as one continuous substance, resembling yellow-green “paint”. Close observation will reveal a minute grainy appearance as the average pollen particle size is under 50 microns, which is less than the width of an average human hair.

As pollen film on water bodies begins to decompose, it typically turns brown/black before eventually dissipating.

This “green paint” phenomenon typically observed on water bodies during the spring is a natural occurrence. Pollination is an essential part of plant reproduction that routinely occurs during the spring season. Levels of visible pollen concentration vary dramatically from year-to-year as a result of seasonal conditions such as temperature, rainfall, wind and other conditions.

Citizens should continue to contact local emergency responders if they see a substance that they have reason to believe is not pollen.