The 45-foot cetacean, which had become beloved by locals and tourists, developed respiration problems Monday afternoon and had trouble swimming upright. It beached itself on a sandbar at about 7 p.m. It was coaxed back into the water but beached itself again.
Photographer Ashala Tylor, who has chronicled the whale's time in the river on her blog, posted this entry Monday night: "Please send love and light or prayers, or just plain good energy, to our beautiful whale, Mama. Tonight she floated down the river towards the ocean and is now caught on a sand bar [at] low tide.
"... Please send good energy and prayers that this wonderful being will either pass on easily or somehow make it out to the ocean. She has graced our river with nothing short of love and dignity and brought thousands of people together to share in her magnificence."
Scientists on Tuesday were conducting a necropsy in the hope of pinpointing a precise cause of death.
"Based on the photos and everything, her fat layer looks good, so we don't think she starved to death," Sarah Wilkin, stranding coordinator for NOAA Fisheries, told the Associated Press. "There's something else going on."
The mother whale entered the river on June 23 with her calf, immediately becoming a tourist attraction. After the calf swam back into the ocean on July 23, facing an uncertain future, marine mammal experts and members of the Yurok Tribe tried many tactics in an attempt to persuade the 40-ton mother whale to leave.
They included water cannon, banging on pipes, chanting and broadcasting killer whale sounds. Tourists serenaded the whale with music and song. Some even prayed while in the company of the whale, hoping "Mama" would leave.
-- Top photo: Yurok Fisheries staff examine the deceased whale located just below the Highway 101 bridge on the Klamath River. The Yurok Tribe, NOAA Fisheries and Humboldt State University are working on plan to remove the whale from the waterway. Credit: Matt Mais/Yurok Tribe
-- Bottom photo shows mother whale with her calf after both had entered the Klamath River on June 23. Credit: Ashala Tylor