The Baltic Sea is no stranger to dead zones. The dead zones are due largely to the Baltic’s limited circulation and strong layering of water, which stop oxygen from replenishing bottom waters. Since the 1950s, nutrient pollution from fertilizer and sewage has caused hypoxia in the Baltic to surge.

According to researchers who study hypoxia in the gulf, extra-dry weather in the corn belt is responsible for the small size of the hypoxic zone, which measures a little under 3,000 square miles – roughly two times the size of Long Island.

According to a new study in Science, the rest of the world fares no better—there are now 405 identified dead zones worldwide, up from 49 in the 1960s—and the world’s largest dead zone remains the Baltic Sea, whose bottom waters now lack oxygen year-round.

Dead zones are caused by excessive nitrogen and phosphorous pollution from human activities, including: Agricultural runoff from farmland that carries nutrients from fertilizers and animal manure into rivers and streams, eventually flowing into the Chesapeake Bay.

What are the effects of harmful algal blooms?

• Produce extremely dangerous toxins that can sicken or kill people and animals.
• Create dead zones in the water.
• Raise treatment costs for drinking water.
• Hurt industries that depend on clean water.

Drinking algae-affected water or consuming food (such as fish or shellfish) containing toxins can lead to gastroenteritis, which can induce vomiting, diarrhoea, fevers and headaches. These toxins may also affect the liver or nervous system.

Harmful algae and cyanobacteria (sometimes called blue-green algae) can produce toxins (poisons) that can make people and animals sick and affect the environment.

Some cyanobacteria (also called blue-green algae) and algae can produce toxins that can make people and animals sick.

Causes and Symptoms of Harmful Algal Bloom-Related Illness

• rash.
• blisters.
• cough.
• wheezing.
• congestion.
• sore throat.
• earache.
• eye irritation.

Algal poisoning is an acute, often fatal condition caused by high concentrations of toxic blue-green algae (more commonly known as cyanobacteria—literally blue-green bacteria) in drinking water as well as in water used for agriculture, recreation, and aquaculture.