A dolphin was pictured and posted on social media by Visit Maldon District, run by Maldon District Council.
The animal was spotted from Maldon Promenade Park this morning. One member of public said she also saw a dolphin from Maylandsea yesterday.
A spokesman for Visit Maldon District said: “If you are visiting Maldon Promenade Park today, look out for a surprise visitor!
“Dolphin spotted this morning at Herrings Point (look left with your back to the statue of Byhrtnoth).”
Dolphins have previously spotted in the area, with a pod of dolphins seen in the River Crouch in North Fambridge in June this year.
Harbour seals and grey seals call the River Blackwater their home and can often be seen from Maldon as they travel down the river.