The church was built around A.D. 390 on the shore of the lake beside the city of Nicaea, as Iznik was then known.
But it was destroyed in an earthquake in A.D. 740 and later became covered in water as the level of the lake changed. [Read more about the ancient church]
The ruined church is built on the pattern of a Roman basilica, which in turn was based on pagan Roman buildings.
The vacuum nozzles remove soil from the underwater site and transport it to the shore, where it can be carefully sifted for artifacts.
The excavations have been carried out by archaeologists from the Iznik Archaeological Museum and Bursa Uludağ University.
A famous place
The city became famous as the site of the first council of Christian leaders, convened there by the Roman emperor Constantine the Great in A.D. 325.
This 16th-century fresco in the Sistine Chapel in the Vatican shows Constantine presiding at the First Council of Nicaea.
But some finds at the site, like these coins from the reign of the emperor Antoninus Pius (from A.D. 138 to 165) suggest the church may have been built over an even older pagan temple.
GALLERY ONLY - Turkey Lake Ruins
The reverse side shows a "Chrismon," a monogram made from the Greek letters chi and rho — the first letters of the Greek word Christos, meaning Christ.
New creative museum
The museum would feature a walkway over the lake to the sunken ruins, a diving center and a glass-walled underwater prayer room in the middle of the church.
If the plans are approved, construction of the museum could begin this year and it could open to the public in 2019.