some lakes have it all of the time or a few hours before sunset and then all night long. its a good thing to have because fish feed on them. supposed to use narrow beam on sonar. use a bigger jig. add more spikes. make it bigger to see in the mess on screen. its like the movie matrix, you have to learn how to read it. they are plankton. they are found in deeper water say over 15 feet.
my new lx-7 deals with it much better than my ice-55 does. not sure why, but glad to have extra time they don't show up. takes about an extra hour or so before they show on screen on the lx-7. turn your settings as low as you can to try to see your jig, if thats not working use it to see fish only and bump bottom and then count cranks on your reel, each crank is about 1 foot. try 1 to 3 feet off bottom. if you see a fish an dyou think its where you are, just wait for it.