The Washington Department of Ecology has fined Foster Farms in Kelso $44,000 for releasing untreated chicken processing wastewater to a treatment plant.
The Three Rivers Regional Wastewater Treatment Plant was overwhelmed by the volume of the waste and some of it reached the Columbia River.
In a statement on Friday, the poultry company says installation of new wastewater equipment led to an "unplanned discharge."
The company says that while its workers attempted to correct the problem, they "inadvertently delayed" notifying the Three Rivers treatment facility.
State water regulations require Foster Farms to pretreat its wastewater before sending it to the plant.
State officials say the processing facility also was at fault for failing to report the release in a timely manner.
The company says it will revamp its wastewater operations and intends to pay the fine.