A system for transport of water between different depths in a body of water is disclosed. The system comprises a sequence of modules constituting a channel, impeller means arranged related to at least one module for contributing to the transport of water, and controlling and guiding means arranged related to the at least one module for controlling and guiding flow of water into or out of the channel. A method corresponding to the system is disclosed. Use of the system and the method related to fanning of aquatic organisms in a bioreactor is also disclosed.