Some 30 protesters were still occupying part of the Corrib gas terminal site in Bellanaboy, Co Mayo last evening to highlight their fears over possible contamination of local water supplies.
Activists made their way on to the site through a gate in the afternoon.
A number of gardaí were on standby during the protest but did not interfere.
The incursion followed an earlier seepage of a brown-coloured liquid from the site. Local streams feed into Carrowmore lake, the source of drinking water for thousands of homes in the Erris area.
A spokesman for Shell E&P Ireland, Christy Loftus, confirmed last evening that the report of a seepage was being investigated by the company as well as by Mayo County Council and the North Western Regional Fisheries Board.
The imminent resumption of full-scale works on the gas terminal proposed for Bellanaboy, Co Mayo, puts Shell on a potential new collision course with objectors.
Some 100,000 cubic metres of bog had been excavated and removed last year when the company decided to suspend excavations and haulage in the face of ongoing opposition.
At a press conference in Castlebar yesterday the company announced its plans to resume the peat haulage operation from early April.