Pony Slough in North Bend , has a air port runway, at the left end in the water you can see a underwater cave, in fact two of them, fascinating folks how far you can see underwater   Very cool

(Used the Google map to find the water nearest, hahahaha as the icon is located some miles from the water

hmmm the icon is situated along Gassy Creek Road, no where near the water, so no hit on location