The Northern Territory's largest waste management and recycling business has pleaded guilty to releasing oil and other contaminants into Darwin's storm drain system.

Contaminants including degreasers from NT Recycling Solutions' (NTRS) site in the suburb of Winnellie entered the storm drain system from the facility's interceptor in March last year, Darwin Magistrates Court heard.

The interceptor is designed to remove hydrocarbon petroleum from stormwater.

The court heard a subsequent investigation and clean-up by the NT Environment Protection Authority (EPA) cost $15,000.

The oil had the potential to cause significant harm to animals and the environment in Darwin Harbour and the Charles Darwin National Park, the court heard.

The company pleaded guilty to polluting the environment with the potential for harm, while its director Leon Schulz pleaded guilty to breaching his environmental protection licence and polluting the environment.

Mr Schulz told the court the company did not intentionally cause the incident.

Contaminants from NTRS entered the storm drain system. ( Supplied: NT EPA )

"I saw no signs there were any issues of any hydrocarbons coming out," he said.

When asked about the affect of the incident, he said he had experienced "a huge amount of personal stress" and was "extremely sad about the incident".

"It's extremely humbling and regretful," Mr Schulz said.

Mr Schulz told the court he considered the company a leader in the market.

"This has a major possibility of damaging our reputation," he said.