The River represents a dose of heroin in the blood stream. The dam represents a means by which to stop or block the flow of water, and in this case heroin. The heroin addict has tried to quit without success. So many failed attempts to quit heroin has made the user second guess himself and his true intentions. Maybe I really don't want to quit?
Layne later revives this meaning while fronting the band Mad Season in the song "River of Deceit" again the river represents heroin in the blood stream. A deceiving Drug indeed! The first few doses feel great and keep you coming back for more. But once your body becomes physically addicted, you no longer use to get high... you use because you have to. It's turned from recreation and into requirement. Your body needs it in order to feel normal. If you don't have it you go through very painful and terrifying physical withdraws. "The river of deceit flows down. The only direction we flow is down." Heroin is infact an opiate which is also considered a downer. The heroin brings you down. Down is a place where you feel no pain. Down is like sleeping awake. And down is a reason to maintain. It can go on for years before it eventually kills you.
On a side note, I can totally relate to AIC and their songs. I am a recovered heroin addict. Heroin changed my life forever and I will never be the same!! If I could take it all back, I most certainly would! I would have never tasted it. When you no longer have it, even in a recovered state, life without it can be miserable and even reduce a persons will to live... It's like there is something missing always. I for one have matured through all phases of recovery, I am blessed to be alive and now humbly accept life for what it is. To anyone thinking about trying it, I plead with you to at all costs stay far far away!! Your just as well to go out and buy a pistol... put three rounds in the chamber... Spin... click... BOOM.