A raceway, also known as a flow-through system, is an artificial channel on land. The water flows from a higher located point to a lower point and flows then back into the river or sea. In raceways there is better control of negative effects compared to net pens. Raceways with water treatment have low impact on the natural environment. Discharge water is treated, which means nutrients are filtered out and bacteria/viruses are killed before the water is released in natural waters.