Mercer Island police are partnering with Seattle Police Harbor Patrol and the U.S. Coast Guard in their ongoing efforts to locate two missing boaters.

On Sept. 2, at about 10:30 p.m., Mercer Island police received a noise complaint. The caller reported music coming from a boat offshore in the 7700 block of West Mercer Way. They told police they began hearing the music at about 9:30 p.m., but it wasn’t until an hour later that they called the police.

Officers who responded in a Marine Patrol boat found while the vessel was still playing loud music, there was no one aboard the red 20-foot “ski type boat.” And evidence — two open and partially consumed bottles of alcohol and two cell phones — pointed to there having been at least two onboard.

The Coast Guard used a helicopter to search Lake Washington, and ground and other marine units searched the water and shoreline, Mercer Island police said. They located a trailer and truck associated with the boat at Gene Coulon Park in Renton.

Law enforcement reached out to friends and family and determined that there was at least one 30-year-old Seattle man and a 33-year-old woman from Burien aboard the boat who are missing. Those missing are James Le and Vanna Nguyen, a close friend of Le’s confirmed.

The man was experienced in operating the vessel and the boat operational, said commander Jeff Magnan, with Mercer Island PD. Magnan said friends and family have indicated that the pair were friends.

They also told police that Nguyen was not a strong swimmer, and when she did swim she used a type IV flotation device, similar to the cushions used on stadium seats. The one onboard was still present when police arrived and they have yet to recover any kind of flotation device from the water.

“We’re not jumping to any conclusions,” he said initially about the ongoing investigation. “We’re just trying to figure out what happened. There’s no signs of foul play. No signs that the boat was hit by another boat. At this point it could just be sad mishap.”

There was no damage to the boat and nothing that would preclude the pair from motoring away, Magnan said. Police have processed and searched the boat. They also examined the two phones left behind, in an attempt to pin down a GPS location of where the phones were last used.

“We have put some hope into the cell phones … to give us some data,” Magnan said. “Unfortunately, even though we were able to get into both phones, neither of them were used past 8:30 at night.”

That’s when Nguyen posted a video on Instagram. Police had already been given the video, Magnan said. After that the data indicates that the boat was somewhere south of the Interstate 90 bridge on the westside of Mercer Island. Their search area falls within these boundaries and stretches to the southern tip.

“Kind of unreal how big of an area we have,” Magnan said. “This is such a huge area and depth.”

What they did discover is that both parties entered waters through the Ballard Locks and traveled into Lake Washington. They then traveled to Gene Coulon Park, parked their boat before going on a bike ride. At some point they decided to take the boat out on the water for a dinner cruise. That’s when the data ends.

Before having this intel, Mercer Island police worked with the Coast Guard to determine drift patterns. Lake Washington has a slight current, Magnan said, as water flows from Cedar River at the south end and eventually flows through Lake Union. They also took into account the wind blowing from the north, northwest. They originally believed the boat had drifted from Seattle’s jurisdictional water and were unsure of how long the boat had been drifting for, before police found it.

“With the unfortunate response with cell phones, we are now concentrating on the areas that we know he has gone to in the past,” Magnan said. Those close to the missing man shared the spots Le would often frequent.

Police have created a picture of what lurks beneath waters using a side scan sonar. So far, they have been able to identify a couple of target areas that will be further examined.

And while others have planned search parties, Magnan said these could hinder investigations. Divers could stir up silt sitting at the bottom of the lake, and cover up areas of interest for police. Recreational divers also put themselves in danger, exploring the deep depths of the lake.

However, Mercer Island Police will continue their efforts to find the missing pair, even as the summer ends and weather patterns shift to fall.

“Just because it’s starting to rain, it doesn’t mean we’re not going to look aymore,” Magnan said. “We’re going to continue investigations and follow any credible lead we get. We are going to continue this until we’ve exhausted all efforts and at this point we haven’t.”