A floating gas-turbine generator meant to alleviate South Africa's crippling power cuts has run into objections by oyster farmers and small-scale fishermen, who fear the environmental damage will destroy their livelihoods.

The seafood sellers fear the 415 MW ship - to be moored for two decades at Saldanha Bay, 140 km north of Cape Town - will pump hot water into the bay and make endless noise, spoiling farmed oysters and scaring off fish as Africa's most industrialised country scrambles to fix electricity problems.

Responding to complaints by the Green Connection environmental justice group, the South African government on June 11 suspended an environmental authorisation application for operator Karpowership in Saldanha Bay. It cited the Green Connection's allegation that Karpowership failed to conduct specialist studies on underwater engine noise.

"Our team believes that this complaint is without merit," Karpowership SA spokesperson Kay Sexwale said on Wednesday.

Saldanha Bay is South Africa's first sea-based aquaculture zone, with 16 new entrants welcomed last year to an industry worth around R1-billion annually, Fisheries Department officials said.

A few minutes from the slipway, multi-coloured buoys and floating black rafts help pinpoint different farm locations, as workers pull up long lines of clinging mussels or exotic oysters fattened in the nutrient-rich waters of the Atlantic Ocean.

"We don't believe it can just be benign, sitting there, because it is generating hot water and it is generating a noise factor which can affect the organisms we cultivate," said Kevin Ruck, owner of Blue Sapphire Pearls oyster farm and a trained marine biologist.

Ruck is worried that hot water discharge from the Karpowership vessel may stimulate harmful algae blooms that could render his succulent oysters inedible.

Started in 2008, his company harvests up to a million Pacific oysters a year, mainly for the domestic market, but also exported live to China.

In February, scientists warned that industrial noise beneath the ocean surface was disrupting marine animals' ability to mate, feed and even evade predators.

But prolonged delays to Karpowership's bid, which includes more ships at two east coast ports, could disrupt South Africa's plan to plug its energy shortfall with 2 000 MW of emergency power.

Karpowership SA said its environmental impact assessments for all three sites "demonstrate little impact to the surrounding air and water environments."

But, for Saldanha Bay skipper Christie Links, the risks are too great.

"Who says the many fish species we depend on will still come into the bay if Karpowership is here?"