Weeds choke Hunyani River


Environment and Natural Resources Management minister Francis Nhema last week told Parliament the hyacinth weeds that have choked Hunyani River were a serious threat to human life and other organisms which depend on the river for life.

“My ministry is aware of the problem of weeds in the Hunyani River over many decades from as far back as the 1970s,” said Nhema during last Wednesday’s question and answer session in the House of Assembly.

“What has made the problem worse over recent years is the high levels of nutrients (phosphates and nitrates) recorded in Hunyani River as a result of raw sewage.”

Chinhoyi MP Stewart Garadhi had asked the minister if he was aware of the threat.

Nhema said hyacinth was a weed listed in schedule five of the Environmental Management Act of 2002, as one of the invasive species.

“It is a perennial water weed which can rapidly increase to form dense mats that reduce water quality, impede flow, and block irrigation channels and equipment. In nutrient-rich waters such as in the polluted rivers or lakes, water hyacinth can grow so quickly that the surface covered by the mats doubles over four to seven days,” Nhema said.

He said to curb the further spread of the weeds, the Environmental Management Agency was now penalising local authorities found discharging raw sewage into water streams.

In 2009, Harare City Council got 47 orders and two tickets for discharging raw sewage into the environment. Nhema said in 2010 the number of orders served to the local authority had declined to seven as a result of the reduction in the occurrence of sewer bursts, which also added to the problem.

He said his ministry challenged researchers to develop an integrated weed management regime that incorporated mechanical, chemical and biological controls in varying combinations and also to use the weed as a new resource for diverse uses as in animal feed, compost, paper and energy from biogas.

Nhema said the problem at hand was water pollution which promoted the growth of the weed and urged local authorities to ensure their treatment plants operated at full capacity all the time.