After conducting research, I was unable to find a boat ramp specifically named "I 94 Mandan" in North Dakota. However, there are several boat ramps located in the Mandan area that can be accessed from Interstate 94.

One such ramp is the Harmon Lake Boat Ramp, located at Harmon Lake Recreation Area in Mandan. This boat ramp services Harmon Lake, which is a small reservoir with a maximum depth of 20 feet. The ramp is described as being "wide" by users on various boating forums, but specific measurements are not available online.

Harmon Lake Boat Ramp permits a variety of watercraft, including motorized boats, kayaks, canoes, and paddleboards. Fish species found in Harmon Lake include northern pike, walleye, and catfish.

It is important to note that information regarding specific boat ramps is subject to change, and it is always recommended to verify the most up-to-date information with local authorities or park officials before embarking on any boating trip.