Thames Water said the huge blockage is at least 100 metres long and will take at least two months to remove.
The mammals will be moved more than 6,000 miles from China to Iceland.
More than 80 people have been injured, five seriously, in Japan after a ferry hit what appears to have been a whale.
The orca whale was spotted in waters more frequently inhabited by dolphins.
Coastguards were called to Loch Eriboll in Durness, northern Scotland, around 12.30pm on Wednesday.
Scientists have used detailed high-resolution satellite images to detect, count and describe four different species of whales.
Experts say the animal appears healthy despite being thousands of miles from home.
Conservationists have reported a fresh sighting of a “very lost” beluga whale in the Thames as they wait to see if it will head out to sea.
A beluga whale has been spotted in the Thames near Gravesend.
The rescue efforts begun after whale became trapped in a fishing net in the waters off the country's coast.