The bulldozer in the pond has gotten into a layer of blue mud (clay). It's very much like molding clay. Soft always a smooth texture. If you ever get into some STOP, then try to get out before you sink. We hit a layer next to a small stream it was 4 feet under surface, then lasted another 6 feet.  4:30 Interesting method to enlarge the pond, but I find an excavator is more effective.  Rule 1: "What in the hell made you think that would work" If you hear that every day, just leave.
Rule 2: Make sure you always have something bigger and badder standing by to save you, if Rule 1 applies to you, but you keep coming back.  I have no idea what the guy at the 05:15 mark was thinking he was doing, but that's a fine way to mess up a lot of people's day trying to get that thing out. Hopefully they had another dozer and/or an excavator there.  The Komatsu dozer in the pond has virtually no grouser bars left on its tracks, this is why he gets stuck. What we used to call ‘dry weather slicks’. Seems the operator is inexperienced and it didn’t occur to him that tracks are no different to rubber tyres....no tread depth equals no grip!  These operators are definitely job security for trailer and machine manufacturers