Rising costs, bureaucracy and fears about child safety are deterring schools from organising trips, according to outdoor education suppliers.
The warning comes less than a month after David Bell, the chief inspector of schools, said that young people were being deprived of outdoor activities because teachers worried that they might be sued if accidents occurred.
MPs on the House of Commons education select committee this week held the first part of an inquiry into the problems surrounding outdoor education.
Organisations including the Field Studies Council (FSC), Outward Bound Trust and the Royal Geographical Society gave evidence suggesting a profound decline in opportunities for fieldwork and other outdoor activities.
The FSC said the number of biology groups visiting its centres had fallen by more than a quarter over the past 20 years. Others reported that fieldwork courses had shortened significantly.
All the organisations complained that schools were being put off trips because they had to fill in more than 15 forms for their local authorities.
The amount of paperwork differed between authorities but often seemed unnecessary as the centres had already been vetted for health and safety standards.
Andy Simpson, head of education at the Royal Society for the Protection of Birds, said it was important to recognise why teachers might be afraid of being blamed for accidents.
"They feel at the bottom of the food chain," he said. "All the organisations around them are covering their own backs, but it's the teacher that feels exposed."
William Ripley, Outward Bound Trust UK operation director, said that press coverage of accidents on school trips gave a misleading impression they were more common.
"When accidents have happened they go right to the top of the profile and parents are worried," he said. "Teachers are very concerned to make sure they have covered every dot and cross."
Rita Gardner, director of the Royal Geographical Society, said that work was needed to convince parents and schools that serious accidents on outdoor education projects were extremely rare. Between 1985 and 2004 there were 57 deaths on school trips, 19 during adventure activities.
Dr Gardner said pupils should be taught about comparative risks. "Five hundred young people die each year falling down stairs while only three or four die on school trips," she said.
Although fear of accidents was cited as a key problem, research by Dr Steve Tilling of the FSC suggests that schools are more concerned by the cost of trips, particularly supply cover and transport.
All organisations feared the workforce deal would increase costs, as schools would need to buy in supply cover rather than rely on teachers to fill in for colleagues on trips. Many said outdoor education organisations in other countries felt the UK's obsession with health and safety was ridiculous.
It was a view shared by MPs on the select committee, who recently went on a fact-finding trip to Scandinavia.
Paul Holmes, Liberal Democrat MP for Chesterfield, said a Norwegian school had shown them pictures of young pupils sitting round an open fire in the snow cooking sausages, an activity that would be considered too dangerous for British pupils.