The Brazos River Authority is encouraging lake and river visitors to have fun but be aware of water conditions that encourage the growth of a "rare but dangerous microorganism.?

Here?s what officials said in a news release detailing concerns:

WACO, Texas ? With summer starting to heat up, people across the Brazos River basin are heading to nearby rivers and lakes. However, the conditions that make the water temperature so delightful can also encourage the growth of a rare but dangerous microorganism.

The Brazos River Authority encourages visitors to enjoy the water, while being aware of health risks associated with swimming in or around stagnant or slow-moving water.

Primary amebic meningoencephalitis (PAM), which is most common during the summer, is a rare disease caused by naegleria fowleri, an amoeba found in almost all untreated, fresh surface water and in soil. The amoeba thrives in low levels of fresh water that is warmer than 80 degrees and stagnant or slow-moving. The PAM infection occurs when water containing the organism is forced into the nasal passages ? usually from diving or jumping into water or from water skiing. The amoeba makes its way into the brain and spinal cord, destroying brain tissue.

Symptoms of the nearly always fatal infection include severe headache, high fever, stiff neck, nausea, vomiting, seizures and hallucinations as the condition worsens. Although PAM is rare ? affecting about one to three people a year in Texas ? those infected usually succumb to the disease within a week.

There were 10 known cases of PAM in Texas between 2000 and 2010, according to state health officials. No cases have been diagnosed in Texas since the beginning of 2011. Worldwide, only a few hundred cases have been reporter over the last 30 years.

To prevent infection, it is recommended that those taking part in warm, fresh water-related activities use nose clips or hold their noses shut while jumping into water. With the amoeba often found in soil, it is best to avoid stirring up underwater sediment. The Texas Department of Health recommends that people avoid stagnant or polluted water and take ?No Swimming? signs seriously.

While the BRA tests for a variety of contaminants, such as E.coli at more than 100 sites, no testing is conducted for the PAM microbe.

PAM cannot be spread person to person nor by drinking water. Swimming pools and hot tubs that are properly cleaned, maintained and chlorinated are generally safe, as is salt water.

For more information contact the Texas Department of State Health Services Public Information Office at (512) 458-7400.