Non-metal breakwaters; non-metal structures for building underwater barriers for seabeds or lake beds; anti-erosion artificial reefs; non-metal underwater structures for fish repopulation; non-metal floating wharfs for mooring boats; non-metal pre-fabricated wharfs; concrete building elements for underwater structures; non-metal poles for underwater constructions; non-metal water pipes; non-metal sheet piles; non-metal beams for underwater constructions; non-metal mooring poles