While the waters of the Penobscot River appear to have cleared in recent days, tensions remain high over the events leading to a massive algae bloom affecting roughly 75 miles of the critically important waterway.

Late last week, the Maine Department of Environmental Protection notified Katahdin Paper Co. that the business’s Millinocket paper mill was being blamed for a bloom of blue-green algae that stretched from the Katahdin region to Hampden.

Katahdin Paper officials acknowledge that phosphorus discharges from the mill likely contributed to the bloom. But there is some dispute between company officials and DEP representatives about what should have happened when phosphorus discharges from the mill increased.

“There was no discussion with us about the decision to dial up the [phosphorus] number,” said Andy Fisk, director of the DEP’s Bureau of Land and Water Quality.

Phosphorus, and more specifically phosphoric acid, is often used to whiten the pulp used to make paper. In Katahdin Paper’s case, the company used phosphoric acid to brighten the glossy “supercalender” paper used for newspaper advertising inserts and other products.

“People want brighter paper,” said Glenn Saucier, spokesman for the company.

The problem with phosphorus use at the Millinocket mill is that some ends up being discharged into the Penobscot River. The additional nutrients, when combined with the summer heat, can lead to a bloom of the type of cyanobacteria commonly referred to as “blue-green algae.”

Some cyanobacteria blooms can produce toxins that, when ingested, can cause irritation of the eyes, ears and skin as well as gastrointestinal problems. Toxic blooms also have been blamed for pet and livestock deaths in other states.

It’s still unclear whether the cyanobacteria bloom in the Penobscot is toxic. Officials with the Penobscot Nation, who first observed the bloom in early August, said Friday that preliminary tests showed it was a genus of cyanobacteria that could produce toxins but that more precise toxicity studies were pending.

The bloom appears to have subsided somewhat, perhaps because of recent rains and cooler temperatures. Nonetheless, leaders with the Penobscot Nation as of Friday were still advising tribal members to avoid swimming in or ingesting the water until the final toxicity results are in.

“Toxins can still be there even after a visible bloom is gone,” said Angie Reed, a water resources planner with the Penobscot Nation’s Department of Natural Resources.

The DEP and other state agencies have not issued any health advisories about the bloom.

Friday was the deadline for Katahdin Paper to file a report to the DEP explaining the circumstances that led to “the excess discharges of phosphorus,” according to the violation notice sent to the paper company last week.

Fisk confirmed the department received the report late in the workday Friday. But he declined to comment because he had not yet read the full report.

But Fisk did state that Katahdin Paper officials indicated they would discontinue significant usage of phosphoric acid after a large blue-green algae bloom in the Penobscot in 2004.

“It was our understanding in discussions with the mill that they no longer needed to use the product,” he said. Fisk acknowledged, however, that small amounts of phosphorus would still be needed in other stages of the papermaking process.

Katahdin Paper representatives offer a different take on the 2004 agreement, which was never put on paper.

“We did not agree to the elimination of phosphorus in our system,” Saucier said. “Would we reduce it? Yes, and we did reduce it.”

Fisk agreed the mill is discharging less phosphorus today than in 2004, but he added that phosphorus levels were excessively high back then. Fisk said he and other DEP staff members are concerned that, after several years of lower levels, Katahdin Paper appears to have increased its phosphorus discharges beginning last winter.

Under the terms of the voluntary agreement, the mill was not required to report discharge levels to the DEP until the end of August. But Fisk insists that, in the interest of open communication and best practices, the company should have notified his agency earlier.

“There is a general expectation that if a mill is going to make a significant process change, … you talk with the DEP,” he said.

In response, Saucier stressed that the DEP did not set specific phosphorus limits for the mill after the earlier bloom but that the company’s discharges remain below the 2004 levels.

Katahdin Paper could still face penalties – possibly including monetary fines – for the algae bloom because its license prohibits it from degrading water quality. As required under state policies, the DEP will work with the company to negotiate a settlement agreement, which would then have to be approved by the Board of Environmental Protection.

If a negotiated agreement is impossible, the matter can be referred to the Attorney General’s Office.