A not to far-fetched guess is that this is some basic phone system used by maintenance personnel. Also, keeping an eye of the floating logs during peak times was probably important and in the event of a log jam, a call could be done upstream to close the nearest gate until the jam was cleared.

Presumably, a portable phone box was attached with clips directly to the wires and call for assistance could be made to a central dispatcher. It is sometimes easy to forget that two-way radio systems with a reasonable range, weight and cost started to become available for commercial use around 1970.