A group of neighbors sued a power plant in federal court for what reason?

The correct answer focuses on the allegation that the power plant is contaminating a river that flows through the properties of the neighbors. This situation presents a federal court matter because it often involves issues of federal law, such as regulations set forth by the Environmental Protection Agency (EPA), or could potentially involve interstate commerce if the river affects multiple states.

When a case arises out of environmental harm, particularly regarding the contamination of an important natural resource like a river, federal courts are likely to have jurisdiction due to federal environmental laws designed to protect navigation, water quality, and public health. Additionally, contamination disputes can involve complex scientific and regulatory issues that are best suited for federal adjudication rather than local courts.

In contrast, the other options pertain more to local issues or state law matters. Allegations of noise pollution and claims of property damage from flooding primarily address local nuisances or property concerns that typically fall under state tort law. Violation of local zoning laws is also generally handled within state or municipal courts rather than federal jurisdiction, as zoning issues are fundamentally about local governance and land use consistent with local policies.