If it is possible to approach the water without going any closer to the mice, do so. Once there, stay out of the water if possible, stay as close to the shore as possible if not, and examine the edibleness of the debris/plants/other things we encounter there.
Debris, especially around the water (and clogging the water path) have been mentioned several times. Some of these debris may be organic. If we do not encounter something strange on the way to the water, and if a wall of mice do not guard it, we can possibly scavenge with safety. That 'log' may be an absolutely excellent banquet of many meals if we can reach it, but it may only look like a log to us who have never seen a log.... it may be something else entire. Anything organic we can reach will be something.
If it is impossible to approach the water here without going any closer to the mice, then move 'upstream' (the way we came) and attempt to approach these 'debris' from that side. If we can approach from that side safely, then explore debris/plants/shore for edibles, staying out of the water as much as possible.
If debris block the water path then debris may have accumulated for a long time, be quite thick, and likewise harbor/hide/offer a ready and easy meal or three.
If it's impossible to reach or find edible debris from the upstream side without disturbing the mice further, then it's pretty clear that it is impossible to enter the water here. So move back upstream, a 'decent distance' from the ecosystem. Enter the water there. Stay submerged for a short time - verify we are as comfortable submerged as we are enclosed by air. If we are comfortable, slowly and without splashes move downstream, attempting to eat a decent amount of debri/plants/algae/other our-sort of food. as we go.