After conducting research, it appears that the boat ramp named 7th Avenue Southeast in Roseau County, Minnesota, is located on the Roseau River. The ramp is open to the public and is suitable for launching small boats, canoes, and kayaks.

There is limited information available online about the specific dimensions of the boat ramp, but it appears to be a single-lane ramp with a concrete surface. There are no reports of any recent renovations or upgrades to the ramp, so it is likely that its dimensions have remained relatively unchanged.

According to the Minnesota Department of Natural Resources, the Roseau River is classified as a Class 1 watercourse, which means that it is suitable for recreational activities such as fishing, boating, and paddling. The river is relatively shallow, with an average depth of around 4 feet, which is why it is best suited for small watercraft.

In terms of regulations, there do not appear to be any specific restrictions on the types of craft that are allowed on the Roseau River. However, boaters are required to follow all Minnesota boating regulations, including wearing life jackets, carrying proper safety equipment, and following speed limits and other navigational rules.

Overall, the 7th Avenue Southeast boat ramp in Roseau County appears to be a relatively small and basic ramp that is best suited for launching small boats and other watercraft on the Roseau River. It provides easy access to a scenic and popular waterway in northern Minnesota.