Couple of years ago the SummerFEST triathlon's run was thorough the flat open area north of the lake. They had mowed 5 - 6 feet wide paths through the tall grass that did not match with any existing trails so it was fun field running. I would only see people's heads and shoulders moving around the green field :)
I have pictures of Anna and Peter in that grass when they were a bit younger and smaller. Pretty funny.
Because of the SummerFEST, I'm not using the NE chunk of the park (basically, everything north of that road that's on the edge of the dog park and segments the park). It's not a huge loss, since a big chunk of that land is out-of-bounds already, or ball fields, or the playground. With thousands of SummerFEST visitors, I don't want to risk crossing that road.
The trails overgrown with grass are some of the side trails south of the lake in that open-ish big reentrant. The trails overgrown with blackberries and nettles are SE of the lake. The trails in the woods are fine.