From the Wisconsin State Journal:
On Lakes Mendota, Monona and Wingra, vehicles weighing over 850
pounds require a special permit, while vehicles weighing less than 850
pounds require flotation and a permit.
On all other Dane County
lakes, vehicles over 850 pounds require a special use permit, vehicles
between 750 and 850 pounds require flotation and a permit and vehicles
under 750 pounds have no restrictions.