There, on the pendant boughs her coronet weedsClambering to hang, an envious sliver broke,When down her weedy trophies and herselfFell in the weeping brook. Her clothes spread wide,And mermaid-like a while they bore her up,Which time she chanted snatches of old laudsAs one incapable of her own distress,Or like a creature native and induedUnto that element.
Forget about using the details (as provided by Gertrude) to help you to determine whether or not Ophelia's death was a suicide or an accident. Gertrude's description of Ophelia's last minutes is a fiction. Just consider this: IF anyone had been close enough to be able to describe the (detailed) steps that led to her death, then that person would have saved her or called for help or at least jumped in to try, thereby "disturbing" the peacefulness (and painless nature?) of Ophelia's last minutes. My point is that no one was there to see the details Gertrude provides. All we can be sure of then is that Ophelia's body is eventually pulled from the stream. Why would Gertrude create this fiction? There are a few reasons. First, she is revealing the news of the death to Ophelia's brother and is -for Leartes' sake - reinventing the (gory) details of a drowning. Second, Hamlet, her son, is responsible for Ophelia's madness (and desire for suicide?), and the Gertrude's description mitigates however slightly Hamlet's responsibility Lastly, and we see this issue developed at the beginning of Act 5, Gertrude's version allows for the argument that Ophelia's death was NOT a suicide. Had it been determined to be a suicide - after all, all we really know is that her dead body is pulled from a relatively quiet body of water - Ophelia would have been denied Christian rites.
Let's firstly talk about the character "Ophelia".
Ophelia is a young noblewoman who is the daughter of Polonius, sister of Laertes and the potential wife of Prince Hamlet. (note the word Prince - King and Prince are different!)
In Hamlet, there are very few female characters (example is Gertrude, who is the Queen of Denmark) and she is one of them. She is a symbol for Prince Hamlet's trust, stability and his sexuality, which factors very importantly in the storyline.
Let's answer the question now : Did Ophelia actually drwon herself on accident?
This could be answered with Yes or No. It depends on how you look at it.
I will say the answer to that question is, "No". There are several reasons behind this answer.
Ophelia's father, Polonius, was killed by Hamlet. (Act 3, Scene 4) And then, Ophelia was insane with her father's death sang some "mad" and bawdy songs. (Act 4, Scene 5). The songs are about her father's death and a maiden losing her virginity - who is, herself, to the Prince Hamlet.
Now, thinking of all the grief and misfortune she has faced, contrast it with Hamlet's quote: "To be, or not to be: that is the question." He wonders if he should commit suicide or live by bearing all the misfortunes of his uncle Claudius marrying with his mother, Gertrude. (This has driven him mad, too!)
Ophelia depicts a reflection of Hamlet, but in a more melancholic way, as well. Being the lover of Hamlet, in the storyline, she already showed herself as the alter ego of Hamlet - potential wife and husband. Imagine if that promise has been broken. Both have turned insane and tragically Ophelia dies.
Where did she die? She died at the willow tree, where she climbed up till she reached the branch. And then, it she falls to the brook and drowns. Most of the time, portrayal of suicide is through falling from the height, and I believe this is not the exception. This shows how unstable she was in her mentality, and same went for Hamlet. However, Hamlet has already discovered the answer that bearing the ills of living is better than going for the unknown world of death. His so-called wife, however, couldn't reach up to that answer.
My conclusion is, she did not go up to the tree without any reason. She went up there, because she wanted solicit self and to get rid of the melancholy she was suffering from.
Answer could easily be "Yes". She died from the accident of the branch breaking, causing to drowning at the brook. This is the simplest answer, just by looking at the situation. This answer is not wrong.
But then, think of it - if you were a normal person, would you go up to the tree of the branch, which looks uncertain to carry your weight? I would say, "No".