The castle is thought to be an Iron Age relic of the Urartu civilisation – also called the Kingdom of Van – which lived in the area from the 6th to the 9th century BC.
The remarkable discovery was made by archaeologists from the Van Yüzüncü Yıl University and a team of divers.
He told the Daily Sabah: “There was a rumour that there might be something under the water but most archaeologists and museum officials told us that we won’t find anything.”
The water levels of the lake had changed over the past few thousand years.
“With this belief in mind we are working to reveal the lake’s ‘secrets’.
“It is a miracle to find this castle underwater. Archaeologists will come here to examine the castle’s history and provide information on it.
“We now believe we have discovered a new area for archaeologists and historians to study.”
Atlantis is a fictonal island first mentioned in the writings by ancient Greek philosopher Plato in 360 BC.