What is illegal to discharge into state or federally controlled waters?

The discharge of trash, oil, or waste into state or federally controlled waters is illegal due to the serious environmental impact it can have. Such actions can lead to water pollution, harming aquatic life, and degrading the quality of the water. Regulations such as the Clean Water Act are designed to protect these waters from contaminants that can pose a risk to both ecosystems and public health.

When we consider the other options, discharging only water is typically allowed as long as it is clean and doesn't contain pollutants. Sewage alone is a significant contributor to water pollution, but laws often encompass a broader range of materials, thus making the option of only sewage too limited. The same reasoning applies to oil, which is a significant pollutant on its own, but the range of illegal discharges is much wider, which is why the correct answer includes all forms of trash, oil, or waste.