CONTIMAINATED seaweed in Sydney Harbour has some of the world's highest levels of copper and lead and is killing sea life that feed on it, a study has revealed.

Up to 75 per cent of the offspring of small crustaceans that feed on a common brown seaweed die.

The UNSW study sampled seaweed from 10 bays ranging from 3km to 11km inside Sydney heads.

The amount of lead and zinc found in brown seaweed in Woolloomooloo Bay, Balls Head Bay and Rushcutters Bay exceed levels found in the Hong Kong Islands and Brazil's Sepetiba Bay - some of the world's most contaminated waterways.

Heavy metals such as copper, lead and zinc end up in Sydney Harbour from stormwater runoff, industrial water and motorised watercraft.

The study is the first of of its kind to draw a geographic relationship between heavy metal contamination in seaweed and the crustaceans that feed on it.

It found that high concentrations of copper in the seaweed species Padinacrassa were associated with low numbers of grazing amphipods - small shrimp-like creatures that feed on the algae.

On average, there are 6,000 animals per square metre of algae bed in the harbour.

"In seven of the 10 sample harbour sites we measured copper concentrations in one seaweed species that exceeded levels known to threaten small crustaceans,'" study author and UNSW biologist David Roberts said.

"These concentrations exceed all previously scientifically reported levels.''

The study is to be published in an upcoming issue of the journal Environmental Pollution