[TOMT] [movie] Possibly Manga (animated) from late 80's early 90's

I rented (VHS) this movie in the late 80's early 90's. I do not remember the name. The animation was kind of Dragonball Z - like.

There was a kingdom and they depended on a careful balance of their water source (the canals which carried it divided the kingdom). As always someone was planning (evil) to get complete control of the source. I am almost positive there was also a curse if the source was tainted.

The protagonist falls in love with the ¿princess? but for some reason, their love couldn't be. Evil promises that he will help him be together with her forever if he helps him and convinces him that the curse and the taint of the source is moot, just old stories.

So this guy obtains the necessary things (¿key to the dam?) to separate the water sources and watches as the canals dry up. After he does, he returns to look for the princess, but all of the citizens and the princess are nowhere to be found and apparently have converted to ¿doves? which fly away (I believe they represent their spirit). As he sees all of his friends and love fly away he realizes that he has been tricked. This moment had a pretty powerful song in the background.

EDIT: Ok, I might have remembered a little bit more. After he screws everyone by releasing the water, he does get to see the princess one last time. She is the one that tells him how the dams work, why they are important and how he has condemned himself to live alone in a world devoid of life (EVERYTHING dies at the release of the water) And why ¿since he could not be patient?, he has now lost her forever. Then she transform into one of this dovey things that fly away and vanishes along with thousands of them.

This might no be completely accurate, but its the best as I can remember.

Thanks in advance for helping me.