Hundreds of craft became stuck at Hickling last summer in the dense underwater fronds of stonewort, a sort of freshwater seaweed with the consistency of a giant Brillo pad, and boatyard owners and yachtsmen fear that this season will be even worse.
But the problem is setting them at odds with conservationists, who regard Hickling as the environmental jewel of the broads and are resisting a programme of weed cutting, which they fear will hurt the area's rare bird, plant and insect communities.
Bitterns, one of Britain's rarest breeding birds, and swallowtails, one of its rarest and most beautiful butterflies, are both found at Hickling, with many other uncommon species such as the Norfolk hawker dragonfly. So the broad is covered by a series of protection designations in European as well as British law.
Feelings are running high, with boatyard owners who complain that their livelihoods are at risk backed by yachtsmen, unable to sail, and the Royal Yachting Association. On the other side, the Norfolk Wildlife Trust, which owns much of Hickling Broad and considers it its flagship nature reserve, and English Nature, the Government's wildlife advisers, insist that conservation is paramount.
Caught in the middle is the Broads Authority, the body with national park status that looks after these normally placid waterways, Britain's largest wetland, which is visited by 5 million people a year, at least 200,000 of whom come for a boating holiday of a week or more.
The authority, which is cutting weed at the moment to keep a channel open at Hickling, plans a wider cut to deal with the stonewort's growth. But this is too much for the conservationists, who say it would breach the European Union's powerful wildlife law, the 1992 Habitats Directive.
This law, which is just beginning to take effect in the UK, concerns the conservation value of the sites it protects - such as Hickling - above all else. It takes no account of boat enthusiasts and their concerns, and it overrides British domestic legislation.
At the heart of the problem is intermediate stonewort, Chara intermedia, which usually forms a dense, interlocking mass on the broad's bed. It is nationally rare, now found only in the Hickling area, and an important food for the large flocks of wintering duck such as shoveller and gadwall.
In 1994 it covered 30 acres of the 320-acre broad, and grew no higher than two feet. But then it began to expand, and last year grew explosively to cover 96 acres and to more than three feet high, in some places breaking the surface. This year it is already a fortnight ahead of where it was in 1998.
The change has come about because aquatic plants in general are flourishing in Hickling as agricultural and sewage pollution is reduced. The stonewort's main rivals, fennel pondweed and water milfoil, have themselves been subject to cutting programmes, thus weakening its competition.
Hickling is large but shallow, and last year's new growth made it virtually impossible for boats and yachts to move outside the main navigation channel. As soon as they did so, their propellers or keels became entangled.
Mike Baker, vice-chairman of the authority's navigation committee, said: "I've been in there with a dory, a rescue boat with a 15hp outboard capable of 20 knots, which has been brought to a complete stop by the weed. What's sailing like? You can't. Simple as that. The stonewort is a dense matted thing, like a bramble bush. You can't go through it."
An independent assessment panel has now been set up to examine the question, and the Broads Authority will make a decision on 28 June.Reuse content