Firefighters tackled several grass and rubbish fires on Bank Holiday Monday.
More than 500 square metres of moorland was found alight near Mitchell's House Reservoir in Accrington.
Crews said the heat and broken glass on the grass could have caused the blaze to start shortly before 5pm.
Earlier on Monday, May 6, firefighters put out a rubbish fire on Maudsley Street in Accrington.
They also dealt with grass fires on a banking close to White Ash Nursing Home in Oswaldtwistle and a small patch of land on Spring Street in Rishton as well as a garden fire on Richmond Hill Road in Accrington.
Trees were also found alight near the Sandy Lane exit to the A56 bypass at around 5.40pm.
Alex Fletcher, crew manager of Hyndburn Fire Station, said: "As the hot weather comes out these fires tend to happen. Some could have been accidental while others may have been deliberate. It was a busy day."