Ophelia felt manipulated by all of the men in her life. Her father, brother, and Hamlet all wanted things from her. She felt like her life would always be like that. She thought Hamlet was acting strange, and her father's death made her depressed. She saw no other way out.
A couple of reasons are that she betrayed Hamlet, she was betrayed by Hamlet, and her father was murdered. Some might say that these things would be enough for a sensitive young woman to become so emotionally distraught that she might lose hold on reality enough or might be overwhelmed by reality to the extent that she might drown herself, not a difficult to do with the long, drapey, heavy clothes women have worn throughout much of history.
The textual evidence (mentioned above) does seem pretty solidly in suicide's corner, but it could still be really interesting to write a creative-critical essay proposing that Ophelia was murdered. It could be in the vein of Tom Stoppard's Rosencrantz and Guildenstern Are Dead. Have you seen the movie version? Definitely check it out!
If you believe the gravediggers, she did kill herself:
Is she to be buried in Christian burial when she wilfully
seeks her own salvation?
They are considered clowns, so we can't take everything they say seriously, but this does seem to suggest that Ophelia definitely killed herself. As to why, I'm not sure other then her world is crashing down around her, her Prince is acting insane and telling her to get away from her, etc.
Honestly she didn't kill herself Gertrude says something about how her dress got wet. I don't know about you but those dresses they wore back then, if anyone got those wet you are sure to be pulled under the water. Give the girls some respect
yeah it is hinted, the fact that they had to hurry up and put her in the ground, almost trying to cover it up and save her soul like the clowns talk about
Poor Ophelia! How confusing it must have been for her, to suddenly have her boyfriend tell her she's basically a whore and that her only option is to join a nunnery. No wonder she lost it. Her brother, who had been her other confidant, had gone away and her father had been killed by Hamlet, her boyfriend. In my mind, there is no doubt that she took her own life, even if she was not in her right mind. The fact that she dies, weighted down by her own skirts, seems to me to be a part of the trap of being a woman in her day. With no one to love her or care for her, and now branded by Hamlet as damaged goods, what is there left for Ophelia? (The scene where she sing-songs and passes out the flowers is creepy.)
As blazedale mentions above, the gravediggers are convinced that she's committed suicide, a mortal sin that would not allow the girl a Christian burial. But there is some ambiguity, I admit, as they do give her a proper burial, but morality seems to me to be the last thing on anybody's mind in this play.
Is it for sure that Ophelia kills herself? I know she drowns in a river, and that she was despondant, but did she actively kill herself? I think it's at least a little ambigious.