If a city or county fails to adopt an ordinance controlling discharges of waste from houseboats within 120 days of receipt of the regional board’s notice pursuant to Section 13903, or fails to adopt or modify such ordinance in the manner determined as necessary by the regional board pursuant to Section 13905, within 90 days of receipt of the regional board’s notice, the regional board may adopt regulations necessary for the control of discharges of waste from houseboats for the area designated. Such regional board regulations shall take effect 30 days from the date of their adoption and shall be enforced by the city or county and have the same force and effect as if adopted as a city or county ordinance.