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Golden Alga (Prymnesium parvum)
Golden Alga (Prymnesium parvum)

Golden Alga

Photo credit:  FWC Fish and Wildlife Research Institute
Photo credit:  Texas Parks and Wildlife

(Prymnesium parvum)

Report this Species!

If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

Golden alga is a naturally occurring, one-celled, microscopic organism that can be found worldwide on every continent except for Antarctica. Toxins produced by this alga have caused extensive kills of aquatic animals, resulting in severe ecological and economic harm.


Golden alga is a tiny organism about the size of a human blood cell. It is very mobile and uses its two “tails,” called flagella, to move through the water. A short, stiff, hair-like structure called a haptonema is used to attach the cell to other cells or objects. A yellow-green, C-shaped chloroplast wraps around the middle of the cell and can be seen under a microscope. During a typical bloom, the water turns yellowish, yellowish-copper, or a brownish tea color. Foaming at the surface of the water in areas where there is a lot of wave action is another sign. Exposed fish may swim slow or erratically just below the surface, lie inactively along the bottom in shallow areas, or show no avoidance to human presence. Other visible signs include redness or hemorrhaging at the base of the fins, around the mouth area, under the chin, and along the belly.

Similar Species

The conditions typical of a golden alga bloom may come from other sources and do not always indicate a golden alga bloom.


Generally found in brackish waters, golden alga cells can thrive in a variety of environmental conditions, including a salinity range of 1-40 PSU (Practical Salinity Unit) and a temperature range of 5-35°C (41-95°F). Other factors that affect its growth include phosphorus (P) and nitrogen (N) levels, cationic substance levels, and pH. Toxic blooms typically occur at salinity levels of 1-12 PSU, temperatures of 10-25°C (50-77°F), and at fairly high P and N levels.


A single drop of water may contain over 2,000 golden alga cells. Unintentional spread may occur by water currents or as cells stick to the feathers or fur of waterfowl and other animals. Under stressful conditions, golden alga is able to form into dormant cysts that can hitchhike to new areas in live wells, bait buckets, recreational boating and fishing equipment, or equipment used during water withdrawals.


First identified in the United States in Texas in 1985, golden alga has since spread to 18 states. In the Mid-Atlantic, it can be found in North Carolina and Pennsylvania, where in 2009, golden alga caused a massive kill spanning nearly 30 miles of Dunkard Creek along the Pennsylvania-West Virginia border.


Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.

Environmental Impacts

Golden alga is fast growing, resilient, and uses nutrients more effectively than other kinds of algae. Bloom situations can cause extreme die-offs of native, threatened and endangered species. Serious economic consequences for affected communities have also been well-documented. At-risk waters can include those with high salinities and those being affected by mineral resource extraction, such as natural gas. There is currently no evidence that golden alga has toxic effects on non-gill breathing organisms or humans.


Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).

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