Here are the pictures showing a pod of whales with Bradwell power station in the background.
The pod of about 30 whales was seen by oystermen in the waters of the Blackwater estuary.
Stacey Belbin, who runs trips in her boat the Lady Grace, was alerted to the unusual visitors by oysterman Stephen Wass.
She said: "I had come back from fishing in the Lady Grace when Stephen told me.
"I contacted my brother-in-law Dale Belbin and we borrowed a boat which was quicker than mine.
"We searched in the River Blackwater near Thirslet where the oystermen dredge but we could not find them.
"We went to the other side of Stone and Osea Island and then came back down the river looking for them.
"Then I got a call from my dad, Gary, saying they were off Mersea Island.
"It was absolutely amazing. They were about 15 to 20 feet long and our boat was only 16 feet. They came right along side us."
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