However, the report says that the level of heavy metals in sewage sludge has halved in the past 25 years because of stricter controls on industrial effluent.

These land-based activities increased the incidence of marine pollution from industrial effluent and poorly managed wastes.

The port has continued to build, adding several more berths, a container terminal, a tanker terminal and an industrial effluent treatment plant.

Today, a large portion of the river's flow originates as municipal and industrial effluent, cooling and process water and storm water overflows.

Major investment in upgrading the sewage treatment works took place, and in the treatment of industrial effluent before it was discharged to the river.