Big Lake is owned by Ducks Unlimited but it is not illegal to ride on it so i dont know why you got that info from them as it's false... Lived here all my life on a farm north of the big lake where the river goes thru my land so i'm positive on that answer.
Like Dale said, it's simple .....
Enter from the south, call the farmer before going there, and dont leave any trash behind... (Does it hurt to pick up a lil trash from someone else who was there previously thats an idiot so we can continue to ride there ?)...