Answer: 26 feet
Step-by-step explanation:
Federal law requires that when a boat of 26ft or more is on lakes, rivers, or in the ocean 3 miles from shore, it should "prominently posted" placards about garbage as well as Oil Discharges stating that oil discharges are not allowed as well as what materials can and are prohibited from being thrown from the boat into the water.
Both placards should be permanently attached with a minimum size of 5*9 inches and made entirely of durable material.
I have attached an example of the placard.