Farmers in Snowdonia are angry at plans to block up drainage ditches on moorland they use to graze sheep.
Keeping water on the Migneint could prevent floods say supporters
The National Trust (NT) wants to stop peat from being washed away but farmers said that could lead to the land on the Gwynedd/Conwy border becoming too wet.
The NT stresses it is an experiment in only one small area, and could even help alleviate Conwy Valley flooding.
But the farmers claim they already lose animals because the land is so wet and blocking ditches would make it worse.
The Migneint area is the second largest of moorland in Wales and is also a special area of conservation.
It is used for grazing mainly sheep and has been criss-crossed by drainage ditches since the 1950's.
Trystan Edwards, National Trust farming advisor, said the idea of blocking up ditches with bales of branches was simply an experiment.
"It is a very small patch and we'll see how it works then we'll sit down and come up with a sound project plan to include much further works," he said.
But farmers think the grazing land could turn from wet moor into full blown swamp.
One, Alun Roberts from Ysbyty Ifan in Conwy, said he was already losing livestock.
"There's a huge problem with sheep drowning and getting stuck in the boggy areas of it," he said.
Another farmer, Idris Roberts, said he was worried blocking the ditches would create more and not less problems.
"It is wet enough as it is and we lose enough sheep already in the boggy parts.
"They should be opening ditches instead of closing them," he said.
The graziers are set to meet at Cynfal Fawr farm near Llan Ffestiniog at 1900 GMT on Wednesday to discuss the matter.