Can I get some help reading the screen?

So i was out today and every 30 seconds or so these lines would constantly be going up till it got to the surface. I'm guessing they aren't fish because it just goes up in a constant line till it leave the screen. Could it be bubbles or something from a spring or weed growth? The ice was well over 14 in thick so if it was a spring I feel like it would be thinner? Possibly bugs but I doubt it would be a bunch of lines going up at once. I'm new to using a graph on the ice and curious on some input? Thanks!