Maybe some sort of cheap buoy network outfitted with sensors, GPS, and a longterm sustainable power source
Idk how feasible that would be and can’t even estimate how many buoys it would take to cover everything
But you could anchor or even connect some of them directly to the pipeline itself. If it’s a network, having every few buoys connected via fiber optic to the pipeline would allow them all communicate and transmit data fast af
Might be possible to collect submarine comms too if the tether acted like an antenna haha