Which type of group would be most likely to lobby Congress to pass a law tightening penalties to businesses that pollute streams and rivers?

The answer is: A public-interest group.

Explanation:

Public interest group Public interest groups can be defined as those groups that pursue objectives whose achievement will apparently provide benefits to the general public, or at least to a wider population than group membership.

Thus, for example, if a public interest group concerned with air quality is successful in its various strategies and activities, the benefit achieved: Cleaner air, is available to the general public, not only to group members.

The answer is: A public-interest group.