The Alaska Department of Environmental Conservation (DEC) has cited six more cruise ships for exceeding effluent limits in Alaskan waters.

Six Princess Cruises ships were found in violation of effluence laws in August, according to the DEC. The ships released illegal levels of copper, ammonia and zinc at least eight times.

The same six Princess ships were found in violation in data collected in May and July, as well as one ship each from NCL, Holland America Line, Regent Seven Seas Cruises, according to DEC data released last week.

Violation notices are sent to the state’s attorney general’s office, which, in consultation with the DEC, will decide whether or not penalties will be enforced.

Discharge limits in Alaska are measured “at the pipe” and not after dispersion, making the state’s effluent laws some of the strictest in the world. To give cruise lines a chance to change management and technology to comply, Alaskan officials are slowly implementing the limits until the full limits are enforced in 2010.