By Nangamso Mabindla
11 October 2005

DRIVEN by a desire to have a cleaner Nahoon River, two learners from an East London high school decided to investigate the dangers caused by the water hyacinth, an attractive free-floating water plant with a pretty blue flower, to the river and life in it.

The two learners, Kyle Lucas and Michael Cole from Hudson Park High School, came second in the National Eskom Science Expo, and gold in the Border region for their school project on the alien invader plant.

For their study, the pair wanted to find out why the alien plant had invaded one of the city's biggest rivers.

"We suspected that residents living in the area were throwing the plant into the river. They normally use it as an ornamental plant, but when it becomes bigger for their containers and ponds, instead of destroying it they dump it in the river," Lucas says.

That is when the problems start, he adds, as the water hyacinth spreads very quickly. Its leaves have swollen stalks that allow it to float, and it spreads by seed. Each flower can have up to 200 seeds.

"The plant grows rapidly and can cover a water surface [quickly]. In fact, it doubles in size in just 18 days," Cole says.

The plant has been declared a noxious weed under the Weeds Act and Conservation of Agricultural Resources Act. According to these acts, no person may grow or trade in water hyacinth.

Landowners have an obligation to eradicate the plant if they find it on their property.

The high school pair say their project aims to educate property owners about the dangers of the plant and ways to eradicate it.

Speaking about the dangers, Lucas says that because the water hyacinth is an invasive plant, it does not have enemies.

"It originates in South and Central America and it thrives in our climatic conditions. But because it is from overseas, it does not have enemies to slow down its rapid growth."

The dense, floating carpet of plant blocks out sunlight, which could pose a danger to life in the Nahoon River. It also restricts water flow in rivers and increases the risk of flooding.

However, there is hope that the plant can be eradicated, and three mechanisms can be used to slow down its growth.

These include:

• Mechanical control - plants are physically pulled from the water and left to die far away from the water's edge;
• Chemical control - a herbicide spray is used. However, the dying plants further pollute the water and the poison affects other plants; and
• Biological control - the plant's natural enemies are imported from South and Central America such as weevils, moths and mites that attack living plants.

However, for the invasion to be defeated property owners need to play their part by removing them from their fish ponds and drying them. Owners need to make sure they do not transport the plant to tips as they may spread seeds in the process.

Talking about the national competition, Lucas says it is an honour to have their project entered with some of the best in the country.

"But we will only be happy if we achieve our goal of educating people about the dangers posed by the plant," he adds.

People can report the presence of water hyacinth and sources of pollution to the national Department of Water Affairs and Forestry on 043 604 5400 and Buffalo City's department of integrated environment and sustainable development on 043 705 9731.