The best description of the energy flow from producers to tertiary consumers in a freshwater ecosystem is:
Producers get 100% energy from the sun, primary consumers get 10%, secondary consumers get 1%, and tertiary consumers get 0.1%.
This option accurately illustrates the concept of energy transfer and loss at each trophic level in an ecosystem. Energy decreases as it moves up the food chain due to inefficiencies in energy transfer, primarily due to metabolic processes and heat loss.