Water level in sump suddenly changed

[DmitryB]

I'm sitting here minding my own business, suddenly my overflow (IM 170 INT) starts gargling. I'm like "That's annoying" I look at the sump and the water level in the first chamber (I haver rollers there) has risen. Anybody have any idea what could have happened? I opened the valve more and the gurgling stopped, but the water level in the first sump chamber is high. I was thinking could something have clogged the regular drain? I have snails crawling into the overflow chamber all the time. I'm sure I haven't caught all of them. What else could have happened?