Conn. Gen. Stat. § 52-448: Not to interfere with existing dams or millsites.

No such dam shall be erected, or watercourse made or altered, to the injury of any mill lawfully existing on such watercourse, or on the stream upon which such dam is to be erected, or from or into which such watercourse flows, or to the injury of any millsite on the same on which a mill or milldam has been lawfully erected and used, unless the right to maintain a mill on such last-mentioned site has been lost or defeated by abandonment or otherwise.