The Girdwood Volunteer Fire Department said the incident happened around 2:30 Friday afternoon near the 20 Mile River bridge along the Seward Highway.
Capt. Josh Heuer said when rescue crews arrived, the woman was stuck up to her knees, and the tide was sweeping in the rate of about one-inch per minute.
Swimmers with the fire department reached her quickly, and freed her within 15-minutes using special equipment, but within that short time the woman had sunk to her waist in the mud, and the water was up to her shoulders because of the incoming tide.
"It was a pretty dangerous situation" Capt Heuer said. "There's definitely the danger of the incoming tide coming in over somebody's head."