What are two examples of nuisance organisms found in water systems?

Nuisance organisms in water systems are typically those that can cause operational issues, affect water quality, or create discomfort for users without necessarily posing a direct health threat. Crenothrix, for instance, is a genus of bacteria known to form biofilms and can create significant operational problems in water treatment facilities by clogging filters and causing other maintenance issues. Nematodes, which are microscopic worms, can also be problematic as they can disrupt biological processes in treatment systems or contribute to unpleasant tastes and odors in the water.

The other options present organisms that can be present in water systems but do not typically fit the primary definition of nuisance organisms. Flies and mosquitoes are more associated with breeding in stagnant water than with the water treatment processes. Worms and larvae can be part of the aquatic ecosystem but are not commonly classified as nuisance organisms in the context of water treatment. Algae and bacteria, while they can cause issues, are often categorized differently, as certain types of algae can lead to harmful blooms, and bacteria can be beneficial or detrimental based on their type. Thus, the choice of nematodes and Crenothrix properly identifies examples of nuisance organisms that may require management in water systems.