Question with trip maneuver under water

[FlameSong]

While I read the underwater combat rule book, it only clarify that a successful trip attack can cause a creature off balance while underwater, which denies that creature's dex bonus on AC and provide +2 attack to its attacker. An off balance creature may attempt a swim check to regain its balance; but it doesn't clarify the DC of the swim check. Also, it doesn't explain how the greater trip functions under water, for example: does using greater trip cause an off balance creature provides attack of opportunity? Thanks for reading my post, I will humblely await your answer.

[CampinCarl9127]

Underwater combat is a nightmare.

I would say the DC of the swim check is the same DC as it would be to normally maneuver in whatever kind of water they are in, which can range from very low to very high depending on if it's something like calm water (DC 10) vs stormy water (DC 20). Perhaps something extreme like a whirlpool could raise the DC further, but I doubt the DC will ever be under 10.

I am unsure of the answer on greater trip. If you could link or quote me the rules where you found tripping a creature causes them to be "off balance", I might be able to at least manage an informed opinion.