The Mississippi Department of Environmental Quality (MDEQ) is issuing a contact advisory for a section of the Pearl River from the Highway 25 bridge to the (Upper Lake) Low Head Dam due to the presence of a Harmful Algal Bloom (HAB).
On September 24, 2025, MDEQ received a report of an algal bloom in the Pearl River upstream of the (Upper Lake) Low Head Dam. MDEQ staff investigated the report and collected samples for analysis. The results confirmed the presence of several species of algae that could be harmful to humans if contact occurs. Because of this, MDEQ advises the public to avoid contact with the affected waters until further notice. Exposure to HABs can pose risks to people and mammals through skin contact, inhalation, or ingestion.
Harmful Algal Blooms develop when nutrients in the water combine with environmental conditions such as slow or stagnant water flow, excessive sunlight, and warm temperatures. At this time, MDEQ is not aware of any unnatural occurrences that may have contributed to this bloom.
MDEQ will continue to monitor the affected area and will revise the advisory as necessary or when conditions improve. See fact sheet below for additional information.
Fact Sheet – Pearl River Harmful Algal Bloom
Q: Where is the contact advisory in effect?
A: The advisory covers a section of the Pearl River — from the Highway 25 bridge to the Low Head Dam due to the presence of a Harmful Algal Bloom (HAB).
Q: Why has MDEQ issued this advisory?
A: MDEQ received a report of an algal bloom in this section of the Pearl River. Samples collected confirmed several species of algae that can be harmful to humans and mammals if contact occurs.
Q: What are the health risks?
A: Harmful Algal Blooms (HABs) can pose risks to people and mammals through skin contact, inhalation, or ingestion. Health effects from contact with a Harmful Algal Bloom vary depending on the type of algae, the amount of exposure, and individual sensitivity but may include rashes, stomach upset, nausea, diarrhea, or vomiting if water is swallowed. Here is more information form the National Institute of Health: https://pmc.ncbi.nlm.nih.gov/articles/PMC8950847/ . MDEQ will coordinate with the Mississippi State Department of Health as needed. MSDH is the lead agency on matters of public health.
Q: What causes Harmful Algal Blooms?
A: HABs develop when nutrients in the water combine with conditions such as slow or stagnant flow, excessive sunlight, and warm temperatures.
Q: Is this pollution-related?
A: At this time, MDEQ is not aware of any unnatural or pollution-related causes that may have contributed to this bloom.
Q: How long will the advisory remain in place?
A: MDEQ will continue to monitor the area and will lift the advisory once conditions improve.
Q: Where can I get more information?
A: Details will be kept updated on our website: www.mdeq.ms.gov. No update means the advisory remains in place.
