Final answer:
The purpose of maintaining a log of water quality checks is to prove that the documentation of water quality checks has been done. Collecting data on various parameters and monitoring the growth rate of trout can provide evidence of the water quality and whether the claim is justified or not.
Step-by-step explanation:
The purpose of maintaining a log of water quality checks is to prove that the documentation of water quality checks has been done. By collecting data on various parameters such as temperature, pH, conductivity, and dissolved oxygen, the log provides evidence of the water quality at different sites. Additionally, monitoring the growth rate of trout in the stream before and after logging can indicate whether the claim of maintaining water quality is justified or not.