Yobs have thrown stones at a harbour porpoise that swam into the canal basin at Gravesend, it has been claimed.

They are said to have pelted the animal last night as it awaited the opening of the gates.

The stone throwing has now been reported to the Kent Police wildlife crimes unit.

Onlookers gathered as the harbour porpoise was spotted in the canal basin on Monday afternoon.

The mammal swam through the open gate but refused to leave.

Attempts to move the creature back out failed until 5am Tuesday when it was high tide again.

The gates to the basin can only be opened by the lock keeper for an hour at high tide.

The porpoise has now made its way back into the River Thames.

Harbour porpoises fully grown can be almost 6ft long.

Experts said they are an increasingly common sight in the river at Gravesend - suggesting this is partly because of good water quality.