Juvenile European eels have been photographed wriggling up a waterfall on the River Ness' upper system in the Scottish Highlands.
The images, including one of the animals crawling in a conga line-like formation, were taken by Ness District Salmon Fishery Board.
Known as elvers, the eels have arrived in UK rivers after migrating 3,107 miles (5,000 km) from the Sargasso Sea near the Bahamas, where the animals spawn and lay eggs.
Ocean currents help to carry the larvae to Europe. One the way the larvae grow into tiny glass eels.
Once in European rivers the eels can grow to up to a metre long, before later migrating back to the Sargasso Sea.
The Ness system involves the largest river catchment in the north Highlands.
The River Ness follows from the northern end of Loch Ness and enters the sea at Inverness.
All images copyright of Ness District Salmon Fishery Board.