The NTSB, working with the National Oceanic and Atmospheric Administration (NOAA) said side scan radar on Thursday "identified targets on the seafloor in the area we expected to find airplane debris."
An official said the NTSB won't confirm that it is the wreckage until it has visual confirmation.
The water depth is 100 to 200 feet and the current is 3-5 knots, so it needs a remotely operated vehicle. It's contacting federal and private partners to find one.
Details, including the cause of the crash, cannot be determined until more of the wreckage is found, according to NTSB.
(Image obtained by FOX 13 Seattle)
Only small pieces of debris have been found so far, partly because of the current and the depth of water in the area.
The Associated Press contributed to this report.