Almost a tenth of footpaths in England and Wales are difficult or impossible to use, according to a survey by walking organisation the Ramblers.
The results of the charity's "Big Pathwatch" found that more than half (56%) of footpaths are well-kept and signposted, but more than a third (35%) were in need of improvement.
Some 9% were difficult or impossible to use, the survey by volunteer "citizen surveyors" found.
The volunteers walked every path in almost half the total area of England and Wales, assessing the condition of footpaths in each one kilometre square area, and recording features found on the paths.
They were also asked to rate how much they enjoyed their walks, and they uploaded more than 46,000 photos to provide evidence of the features they had reported.
More than half the features - some 59,000 - were negative, including muddy, ploughed or potholed paths, unsafe stiles, gates or bridges, heavy undergrowth, overhanging plants and trees, and particularly missing, broken or misleading signs.
But 45% of features were positive, with attractive views coming top of the list.
The Ramblers said that while local authorities were responsible for maintaining paths, rights of way were competing with other services for funding in increasingly squeezed council budgets.
There has been a 20% cut in the workforce looking after footpaths over the last five years, the Ramblers said, and everybody had a part to play in looking after them.
The charity's director of advocacy and engagement, Nicky Philpott, said: "Walking is great for our health and mental well-being. It's a cheap form of transport and exercise, and a well maintained path network could provide the solution to some of the country's biggest challenges.
"The results of the Big Pathwatch show that while many paths are well-kept, a significant number are in serious need of improvement, with many of these completely blocked or very difficult to use, resulting in people having to abandon their journey and turn back."
She said the Ramblers should be at the forefront of solving problems, working with local authorities, using findings from the Big Pathwatch and deploying the charity's volunteer path maintenance teams to help maintain "this key community asset".
And the public could help, by getting out and walking local footpaths, reporting problems to the Ramblers, or joining the Ramblers path maintenance teams to help keep rights of way clear, she said.