Green algae has been washed down the Nahoon River following heavy rains this week.
East London museum natural scientist Kevin Cole confirmed it was algae but could not confirm what type it was.
“I unfortunately cannot identify the species as it may be an unknown … I also cannot confirm whether or not this is an exotic species,” said Cole.
He said there were a number of environmental reasons for the algae.
“Algal blooms happen through a combination of conducive environmental factors such as nutrient enrichment [nitrogen and phosphorous], water temperature, adequate intermittent high light intensities and stable water columns,” he said.
Cole said nutrients are normally deposited in the water by erosion from the surrounding banks and sewage waste as was the case with the Nahoon.
“So the nutrient enrichment of the Nahoon is mostly caused by humans. Household cleaning products can also contribute to high nutrient levels,” said Cole.
He said lack of rainfall in the past months was another factor which could have lead to the proliferation of green algae.
“The lack of rainfall in recent months has contributed to low turbidity in the river system and stable water columns allowing light to penetrate and less mixing of water in the river system,” he said.
Cole said algae did not pose a direct threat to the environment.
“This does indicate that the river has been enriched by nutrients and the most likely are those related to sewage and run off from agricultural lands, but the algae will die off when in contact with the higher salinity levels downstream where sea water will mix with the fresh water,” said Cole.
He said in exceptional circumstances algal blooms could create anoxic conditions in freshwater ponds and dams which lead to a die-off of fish and other species due to low oxygen levels in the water.
He added that the algae should die off and be washed out to sea with the normal estuarine dynamics of the river.
East London water specialist Wayne Selkirk said changes in the ecosystem such as birds moving in between different systems, often caused the introduction of exotic plant species, such as those found in the river.
“The green stuff you see in the river is not just algae but there are also other plants such as the water hyacinth and the water fern which are both fairly harmless,” said Selkirk. — firstname.lastname@example.org