A Long Island man is believed to have drowned while kayaking with his fiancée in a Washington state two days after their engagement — heroically pushing his bride-to-be to safety before vanishing in the frigid waters.

Travis Valenti, 37, of Massapequa, was last seen when his kayak overturned on Lake Crescent in Olympic National Park around 2:10 p.m. local time on June 9, the National Park Service (NPS) said.

Valenti’s fiancée, Marlene – who he proposed to just two days earlier – tried to help him out of the cold water, but was forced to swim to shore when her own kayak tipped, the statement explained.

His brother said Valenti pushed his bride-to-be to safety before going missing.

“It started out as the best trip of their lives and took just a tragic turn that nobody could really see coming,” Valenti’s brother, Austin, told News12 Long Island of the tragedy.

“Travis gave [Marlene] the extra little push that she needed to get safe, and they still haven’t found him since Friday at 2 or 3 p.m.,” he continued.

Neither Valenti nor his fiancée were wearing life jackets. Valenti was lost about a quarter mile offshore at a depth of 400 to 500 feet.

Workers at the nearby Log Cabin Resort immediately initiated a search, but were unable to locate him. Another search the following day also failed to turn up his remains.

Friends of Valenti’s family set up a GoFundMe to finance additional searches. As of Wednesday afternoon, the fundraiser had raked in over $20,000.

“He was just everybody’s favorite guy, including Marlene’s and all of ours, they were just a beautiful couple, and they had this beautiful life planned out and it just gets cut so short out of nowhere,” his brother said.

Valenti grew up in Baldwin and worked for the financial services company Two Sigma at the time of his death, social media posts indicate.

Lake Crescent in the second deepest lake in Washington, with depths of up to 624 feet, according to the Department of Natural Resources.

In its statement on Valenti’s death, the NPS warned that the lake has surface temperatures around 50 degrees Fahrenheit at this time of year.

“Sudden immersion into cold water will impact a person’s breathing and over time, their ability to move extremities. Swimmers are encouraged to use a buddy system,” the caution read.

“Boaters should always wear a life jacket and understand the risks of recreating on large bodies of water, such as underwater hazards, wind, waves, and water temperature.”