What is the purpose of a forward sweeping motion when collecting water samples from a stream or lake?

The forward sweeping motion when collecting water samples is primarily intended to prohibit contamination from the sampler's hands. This technique helps ensure that the sample represents the water body being tested rather than being influenced by any substances or contaminants that may be present on the sampler's hands. By sweeping the container forward while drawing water, the sampler minimizes the risk of introducing any external pollutants into the sample, thereby maintaining its integrity for accurate testing and analysis.

While the other options may involve considerations during sample collection, they do not specifically address the key purpose of the forward sweeping motion. For example, equal mixing can occur more effectively with other sampling techniques, and preventing trash collection is not the primary focus during this type of sampling. Creating a current might aid in sample gathering but is not the central goal of this particular motion.