The alarming sight of large clumps of seaweed floating off the west Dorset coast sparked calls to coastguards from worried onlookers.

A dead whale, an upturned boat, pollution – all these were suspected and prompted people to raise the alarm.

Coastguards initially described it as an "Unidentified Floating Object (UFO)".

West Bay Coastguard Rescue Team was called out twice in the space of a few hours to investigate the mystery sightings of "floating dark patches".

Following investigations, officers put it down to patches of seaweed drifting with the tide.

The first callout on Friday morning was to Seatown where members of the public reported possible pollution out at sea.

A spokesman for West Bay Coastguard said: "Officers observed a number of large floating dark patches on the surface of the water, but closer inspection revealed that these were in fact very large clumps of seaweed drifting with the tide.

"This was logged as a false alarm with good intent."

In the early afternoon the team were out again, this time to Chesil Beach at Abbotsbury where there were reports of "a large object floating in the sea".

A member of the public had reported that the object was "around 20-30 metres long and protruding around two metres out of the water".

They were unsure if it was a dead whale or the hull of an upturned vessel.

While coastguard officers attended, the Navy was contacted by Solent Coastguard co-ordinators to see if they had any boats or submarines in the area.

The coastguard spokesman said: "On arrival at Abbotsbury, officers scanned the sea to find no trace of any vessels in distress, or any vessels at all for that matter.

"They did however observe some more very large clumps of seaweed floating on the water surface similar to those found earlier in the day towards Seatown.

"With the Navy not having any vessels in the area and no-one being reported in distress, Officers left the scene.

"It was noted that all along our area of coastline, there seemed to be multiple large dark patches of floating seaweed which we put down to the day’s callouts."