I did my open water dive training and certification course while I still lived in Oregon. The first part of the course was done in the local municipal swimming pool at night after it closed. I remember vividly sitting with 8 or so other students and two instructors on the bottom in the deep end. The bottom six inches of the pool were covered with this gelatinous mixture of snot, spit, piss and smears of brown material. That was in 1986. I have never been in another pool.