After conducting research, it appears that the boat ramp named Severn Avenue 801-1399 is a public boat ramp located in the City of Tampa, Florida. It is situated on the west bank of the Hillsborough River, which flows through the city and empties into Tampa Bay. The exact address is 1050 Severn Ave, Tampa, FL 33606.

According to the City of Tampa's website, the Severn Avenue boat ramp is a single, concrete ramp that is 20 feet wide and 150 feet long. The website also states that the ramp is suitable for small boats, including canoes, kayaks, and jon boats. However, it is not recommended for larger vessels, such as powerboats or sailboats.

As for the body of water that this boat ramp services, the Hillsborough River is a popular spot for recreational boating, fishing, and other water activities. The river runs through several parks and nature preserves in the Tampa area, including Hillsborough River State Park and Lettuce Lake Regional Park.

It is important to note that information regarding boat ramps and their specifications can change over time, so it is recommended to double-check the latest information before planning a boating trip.