Why Did Isildur Cross the River?

[Inziladun]

Hint: the answer is not 'to get to the other side'.

This has to do with the movements of Isildur leading up to his loss of the Ring, as described in the Unfinished Tales chapter, Disaster of the Gladden Fields.
After the fall of Sauron at the end of the Second Age, Isildur was returning to Arnor by way of Rivendell. It had been decided to travel north into Wilderland and make for the 'High Pass' through the Misty Mountains, i.e., the same pass used by Thorin and Co. in The Hobbit. That way was chosen over the Gap of Rohan apparently due to the latter being a longer route, which it would have been.
In the event, we know that Isildur and his guard were ambushed in the Gladden Fields by Orcs, and he put on the Ring to escape them. He tried to swim west across the Anduin but was forced by the current back into the weeds along the East-bank. The Ring left him, and he was shot and killed by Orc-arrows.
Here's the question: Was it really necessary for him and his men to have been journeying on the east side of the River? It is plain from the narrative that they did so. They set out from Osgiliath, and plainly could have chosen to travel on the western side if they'd wanted. Why didn't they? It would have meant passing very near or through Lórien, but surely that would have been allowed of the Dúnedain, kin of Elrond and recent allies of the Elves in battle. For that matter, if they'd gone through Lórien, they could likely have crossed the Mountains through Khazad-dûm, I think.
Insights?

[Ibrîniðilpathânezel]

Originally Posted by Inziladun

Hint: the answer is not 'to get to the other side'.

Aw, shucks.

Offhand, the only reason I can think of is that it is an example of Isildur's hubris. In his mind, he probably felt that with Sauron defeated and himself in possession of Sauron's Ring, there would be no longer be any danger from orcs. Given the pride that led him to keep the Ring against all counsel, he was vulnerable to the Ring's desire (if such it can be called) to return to its Master. Having Isildur take the less safe route along the river would work to its advantage, since it put him more directly in harm's way -- and on the quickest path for the Ring to be regained by the enemy. That's my thought, anyway.

[Rumil]

I expect Ibrin has the right of it.

Although perhaps the Gladden Fields were more marshy and thus impassable on the Western side, making it a sensible idea to go along the Eastern bank of the Anduin. As long as no interference from Dol Guldur was expected.

Of course at this stage it was still Amon Lanc, and Sauron had not yet occupied the place.

[Inziladun]

Originally Posted by Ibrîniðilpathânezel

Given the pride that led him to keep the Ring against all counsel, he was vulnerable to the Ring's desire (if such it can be called) to return to its Master. Having Isildur take the less safe route along the river would work to its advantage, since it put him more directly in harm's way -- and on the quickest path for the Ring to be regained by the enemy. That's my thought, anyway.

According to the UT chapter, the Ring was a probably a factor in causing the Orcs to attack with greater courage and ferocity than they ordinarily would have; it called to Sauron's servants.
In LOTR we see it apparently acting in answer to other wills in concert with it, while they are in its vicinity. An example might be it slipping onto Frodo's finger at the Prancing Pony, in order to reveal itself.
However, would the Ring be capable of planning Isildur's route for him, knowing some of Sauron's forces would be waiting for the Dúnedain hundreds of miles away? The Orcs that ambushed him were part of a small, forgotten detachment, whose sole purpose seems to have been to waylay any enemies they outnumbered.

Originally Posted by Rumil

Although perhaps the Gladden Fields were more marshy and thus impassable on the Western side, making it a sensible idea to go along the Eastern bank of the Anduin. As long as no interference from Dol Guldur was expected.

Possibly, but they still could have made use of Khazad-dûm or the Redhorn Gate and avoided the Gladden Fields entirely.

[Boromir88]

I wouldn't say it was Isildur's pride which led him to pick his route, and I would not overestimate the sway the Ring may have played.

"I cannot use it. I dread the pain of touching it. And I have not yet found the strength to bend it to my will. It needs one greater than I now know myself to be. My pride has fallen. It should go to the Keepers of the Three."~Unfinished Tales: Disaster of the Gladden Fields

Isildur's failure to master the Ring, appears to have caused a significant blow to his pride. To the point where he is no longer boasting about being the one who dealt the "death blow," and claiming the Ring as an heirloom, but seriously contemplating handing it over to Elrond. Whether Isildur would have followed through or not is another question, but if the Ring could pick up that Isildur was taking it to Rivendell (a dangerous place for the Ring to end up!) then it could have played a factor. Afterall, it did seem to draw the orcs attention.

[alatar]

Are we asking why Isildur, when under attack, went for a swim? Or why he was doing his Middle Earth victory lap? If it's the former, I'd think that it not only might have saved him, but aided his escape as don't the evil folk fear water, to some extent?