Long article with much information:
The pilot did not report trouble or issue a mayday, and the plane disappeared from flight-control radar screens. Only one body has been found.
www.seattletimes.com
From the article, keeping within the 10% copyright rule:
Hours later, the family of three of those presumed dead identified them as renowned Washington vintner Ross Andrew Mickel, the founder of the Eastside-based
Ross Andrew Winery; his wife, Lauren Hilty; and their 22-month-old son, Remy.
Also aboard the plane, according to The Spokesman-Review, was Spokane civil rights activist Sandy Williams, 60, who founded a community center and Black newspaper in that city.
...
“We are deeply saddened and beyond devastated at the loss of our beloved Ross Mickel, Lauren Hilty, Remy and their unborn baby boy, Luca,” read a statement issued Monday night by the Mickel and Hilty families. “Our collective grief is unimaginable.” The statement went on to express gratitude to the searchers and other friends and supporters.
...
Officials believe the wreckage is on the seafloor, which is between 150 and 200 feet deep in that area.
...
Little information on the cause or circumstances of the crash was available. The pilot did not report trouble or issue a mayday, and the plane just disappeared from flight-control radar screens.
...
“We anticipate that there will be continued debris and other things washing up,” said Giard, who urged coastal dwellers, residents and tourists to report any debris that comes ashore.
...
One resident of Bush Point gave the Coast Guard a saucer-sized piece of foam that reeked of fuel. Later, a piece of metal debris was found near the decrepit wharf of the former resort.
...
In the water, rescuers found a seat from the plane, stray life jackets, sheets of aluminum, a page from some sort of log including the plane’s tail number.
...
The plane was flying at around 600 feet, at a speed of roughly 140 miles per hour, which means its plunge into Puget Sound occurred in just seconds.
...
Giard, the Coast Guard search and rescue spokesperson, said the Otter on Sunday was being tracked by its owner, who had tried to contact the pilot by radio as the plane veered slightly toward Port Townsend and then stopped tracking. No contact was made.
Passengers on another seaplane in the air at roughly the same time and in the same general area as the missing Otter reported a turbulent flight.
=== More at the link.
A woman on the other seaplane reported that the passenger pickup point (Cortes Island) of her flight had to be changed due to choppy waters and during her flight the plane dipped and lurched. She posted on her social media about it but took the post down when she heard of the Otter crash.
The article listed some information on other crashes involving the de Havilland DHC-3 Otter floatplane. In general the Otter is considered a well-built plane and as
@Seattle1 said a common bush plane in Alaska, here in Washington and in South America. Age and saltwater are two factors that can affect performance but pilot error hasn't been ruled out. I'm not sure if the cause will ever be determined. MOO.