Pennsylvania environmental officials are investigating whether this week's fish kill in Skippack Creek was caused by the same Montgomery County meat-processing and rendering plant blamed for three others in the last two years.

As many as 3,000 fish, mostly minnows but also white sucker and bass, along with frogs and bullfrog tadpoles, worms and leeches, were found dead late Wednesday afternoon in a mile-long portion of the creek just below the Moyer Packing Co. (MOPAC) in Franconia Township.

In that same stretch of the 15.2-mile stream that begins in Souderton and flows southwest to the Perkiomen Creek, about 10,000 fish could not survive an Aug. 9 onslaught of untreated wastewater containing a high level of ammonia that robbed the stream of dissolved oxygen. Last year, the death of about 700 fish - some from ammonia, others from untreated wastewater - in two incidents resulted in nearly $80,000 in fines for MOPAC.

This week, the killer was chlorine, found in high amounts in the Skippack when the dead fish were discovered. As of yesterday, the state Department of Environmental Protection had identified only one potential source.

"We do know that there was a high level of chlorine in the stream, and we also know that at the MOPAC facility, there was a problem with their chlorine-disinfection system that used too much chlorine in their plant on Wednesday," Dennis Harney, a DEP spokesman, said.

He said DEP water-quality experts were "gathering any information that may help us to definitively link the fish kill to a specific source."

Yesterday, a MOPAC executive said it had not been determined that the plant, which employs more than 1,600 people, was that source.

"We reported [the kill to DEP] and we're working with them to identify whether we were the cause or there was another cause," said Mark Linzmeier, executive vice president of Smithfield Beef Group of Green Bay, Wis., MOPAC's parent company.

The contaminated portion of the creek, from just north of Schoolhouse Road downstream to where the Skippack crosses Cassell Road and the Pennsylvania Turnpike Northeast Extension, is just below the discharge pipe for MOPAC's wastewater treatment plant, Harney said.

It is the same stretch where illegal discharges in June and September 2006 killed about 700 fish.

In October, MOPAC agreed to pay DEP and the state Fish and Boat Commission $77,888 in fines for the 2006 incidents - one the result of power outages, the other because a trench drain that carries wastewater from the beef processing plant became obstructed by manure, mud and other debris. Five months earlier, DEP fined MOPAC $61,000 for air-quality violations at the rendering plant.

In addition to the hefty fines for the 2006 fish kills, MOPAC entered into a consent order and agreement with DEP and the Fish and Boat Commission. It requires the company to overhaul its wastewater treatment plant, which is permitted to discharge up to 750,000 gallons of treated effluent into the creek per day.

Harney said the company had submitted a permit application for DEP's review. The upgraded facility is expected to be functional by 2010.

A malfunction of the treatment plant caused the massive fish kill in August. Whether that will lead to more fines and/or other penalties for MOPAC has not been determined, Harney said.

He said all four Skippack Creek spills are "serious incidents that we don't take lightly" and expressed confidence that the renovated wastewater plant would go a long way to preventing future kills.

Until then, Harney said, "we will also have to consider any measures that we as a regulator or MOPAC as the operator can do to minimize the likelihood of this sort of event until that plant comes on line."

MOPAC is committed to such prevention efforts, Linzmeier said, adding, "We have the best interests of Skippack Creek and the environment in mind."

Contact staff writer Diane Mastrull at 610-313-8095 or dmastrull@phillynews.com.