More than a million fishermen in Sri Lanka's north-east may have lost their livelihoods in the Asian tsunami, experts say.
Ten of the country's 12 cooperative fishing harbours were hit
About 80% of fishing boats there are believed destroyed and many fishermen are also too scared to go to sea.
The Tamil Tigers who hold some areas say the government has not shown it is committed to giving aid.
An advance party of 42 US marines to help aid efforts has landed in Sri Lanka where 30,000 have died.
Some one million Sri Lankans are estimated to have been displaced by the tsunami which struck over a week ago.
The team of marines, bearing heavy equipment and helicopters, is expected to pave the way for the arrival of a further 1,500 US soldiers.
The BBC's Frances Harrison in northern Sri Lanka says nobody there is eating fish, once a mainstay of the diet, even if it has been landed.
Some reports say one reason is that people believe the fish are feeding on human corpses washed out to sea.
Those who are assessing rehabilitation needs say they will not allow people to live within 300 metres of the shore from now on for their own safety.
But our correspondent says they are also not sure if people will want to go back to the coast without assurances that some sort of warning system is in place.
Fishing officials say 10 of the country's 12 co-operative fishing harbours were damaged.
The Tamil Tigers, who hold areas in the north and east, have expressed fears that the Sri Lankan government's claims that it wants to work with the rebels on relief efforts is propaganda and in practice it is not doing so.
The head of the rebels' political wing, SP Thamilselvan, told the BBC in the northern town of Kilinochchi that the Tigers were now having to rely on international aid agencies.
He said he hoped the international community would not let the fact the Tamil Tigers were a prescribed terrorist organisation affect humanitarian relief work with them.
President Chandrika Kumaratunga dismissed that criticism.
She told the BBC her government had sent far more aid to rebel-controlled areas than to the predominantly-Sinhalese south of the country even though she said many more people had died in government-controlled areas.
The Tigers estimate 30,000 are dead or missing in the areas they control, and more than 500,000 displaced.
The rebels say they have moved in teams to bury corpses and control the spread of disease but lack the heavy equipment required to remove debris.
Further south on the east coast, in Ampara, aid has begun getting through following the weekend's flash flooding that hampered relief efforts.
There, a Tigers colonel said his forces were working with the government's Special Task Force police.
"Their work has been commendable in that region. We are able to solve problems in dealing with the crisis at a local level, " Colonel Bhanu said.
The BBC's Dumeetha Luthra in Ampara says food is only now arriving for some of the isolated villages.
In Galle, on the southern coast, authorities were expecting US marines to set up an operation.
About 1,500 American troops are soon expected to be deployed in Sri Lanka. Transport planes have already brought in generators and vehicles.
Seven Indian ships are helping in the south and east. Delhi has also flown in tents for Jaffna in the north.
Aid trucks are often mobbed by people wherever they stop.
However, aid officials say there should be more co-ordination of donations because some unnecessary items are taking up precious space.
"We have bags and bags of pepper, for example, which simply isn't a necessity," said John Carlton, of ActionFast.
Chris Weeks, director of the World Economic Forum's Disaster Resource Network, said more short-range aircraft were needed to transport supplies.