Swamped

You consider following her to see where she's stationed, but decide against it. You've spent too long away from the group as it is. Besides, the longer you take, the more time she has to spot you.

Instead, you decide to take advantage of the fact that the walkway is under the water. You listen carefully for Greeneye's footsteps, to work out where she is, then you leap out, blade drawn, and strike.

The walkway, that is. You know well that it's common for there to be weak spots after the rain, and the Marshguards don't have as many resources for repairs. If Greeneye falls in, it won't draw suspicions.

She cries out for help as she plummets, but you've already grabbed her and started back for the underbrush. More guards might come running, but they likely won't think to check over there.

You've got enough time to grab her, releasing your aquablade as you do. It starts floating up, but you manage to catch the strap with your foot.

Of course, Greeneye doesn't intend to get caught without a fight. She's already struggling. You try to swim as best as you can despite the struggle.

She had the sense to wear her mask in case of an accident, but even so, you're sure you can hold out until she loses consciousness from the pressure difference underwater. But that would be very bad for her body. You'd prefer a gentler approach.
But you're also pressed for time. You don't want the group moving on without you, or worse, risking themselves to find you. You can hear three sets of footsteps on the walkway; they're some distance away, but clearly they're going to check the hole you left.

What's your best option here?