Strange tracks

Every time I pass the sluice gate I check for tracks to see if an otter has been by.  The orange algae, or whatever it is, regrows in 24 hours or so and wipes out older tracks.  As well as otter prints there are often water rail and moorhen prints and scrape marks from floating branches but on one occasion several weeks ago there were some very strange marks.  They appeared when the water was very shallow and whatever made them didn't trigger the trail camera.

In the photo above you can see otter prints near the camera and three sets of wiggly lines on the far side, possibly or perhaps not related to the slightly diagonal lines.  Here is a closer view.

I have kept a close eye out but the marks haven't reappeared, perhaps because of the prolonged heavy rain which has meant the water is much deeper.  I haven't been able to work out what has produced these marks.  My best wild guess is an eel, swimming upstream against the current in very shallow water but that may be way off and searching online produces no useful result.  If you know, or can make a better guess, please leave a comment.