[fostermom]

I found two organisims listed that can be obtained by swimming in contaminated water...toxoplasmosis that can affect the brain, and cysticercosis that can cause seizures and psychotic behavior...long shot but more as an fyi:

How do people get cysticercosis?
People get cysticercosis the following ways:
By consuming food or water contaminated with the eggs of T. solium (pork tapeworm). Worm eggs hatch and the larvae then migrate to various parts of the body and form cysts called cysticerci. This can be a serious or fatal disease if it involves organs such as the central nervous system, heart, or eyes.
By putting anything into your mouth that has touched the stool of a person infected with T. solium.
Some persons with intestinal tapeworms may infect themselves with eggs from their own feces as a result of poor personal hygiene.

Symptoms of cysticercosis
Symptoms may vary depending on the organ or organ system involved. For example, an individual with cysticercocis involving the central nervous system (neurocysticercosis) may exhibit neurological symptoms such as psychiatric problems or epileptic seizures. Death is common.
When will symptoms appear? What is the duration?
Symptoms usually appear from several weeks to several years after becoming infected with the eggs of the pork tapeworm (T. solium). Symptoms may last for many years if medical treatment is not received.

Who is at risk for contracting cysticercosis?
Persons traveling to countries where sanitation may be substandard and the water supply may be unsafe.

Persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or those individuals undergoing chemotherapy may be at a greater risk for infection.

How to prevent cysticercosis

Drink water only from treated municipal water supplies.
When traveling to countries where the water supply may be unsafe, either avoid the water or boil it for 1 minute to kill parasite eggs. Drinking bottled beverages or hot coffee and tea are safe alternatives.
Do not swallow water while swimming.
Do not swim in community swimming pools if you or your child are infected with tapeworms.
Wash, peel, or cook raw fruits and vegetables before eating.
Make sure that infected individuals wash their hands frequently to reduce the spread of infection.

Toxoplasma gondii

How do people get toxoplasmosis?
People get toxoplasmosis the following ways:
By consuming foods (such as raw or undercooked meats, especially pork, lamb, or wild game) or drinking untreated water (from rivers or ponds) that may contain the parasite.
Fecal-oral: Touching your hands to your mouth after gardening, handling cats, cleaning a cat's litter box, or anything that has come into contact with cat feces.
Mother-to-fetus (if mother is pregnant when first infected with T. gondii).
Through organ transplants or blood transfusions, although these modes are rare.

Symptoms of toxoplasmosis and severe toxoplasmosis
Toxoplasmosis is relatively harmless to most people, although some may develop "flu-like" symptoms such as swollen lymph glands and/or muscle aches and pains. In otherwise healthy individuals, the disease is usually mild and goes away without medical treatment. However, dormant tissue stages can remain in the infected individual for life.

However, persons with weakened immune systems such as those with HIV/AIDS infection, organ transplant recipients, individuals undergoing chemotherapy, and infants may develop severe toxoplasmosis. Severe toxoplasmosis may result in damage to the eyes or brain. Infants becoming infected before birth can be born retarded or with other mental or physical problems.

When will symptoms appear? What is the duration?
The time that symptoms appear varies, but generally symptoms will appear 1 week to 1 month after consuming the parasite.

The duration of the illness depends on the health and immune status of the host. Persons with weakened immune systems may experience illnesses of long duration, possibly resulting in death.