Nauticus Robotics is building undersea robots that can reduce costs and emissions in offshore industries. The Aquanaut robot developed by former NASA engineers can perform monitoring and maintenance tasks at half the cost and with nearly zero emissions. The robots can travel underwater for up to 24h
https://www.reddit.com/gallery/11dhy5oTJ-FlyingFish drone flies through the air and "swims" underwater
https://newatlas.com/drones/tj-flyingfish-aerial-underwater-drone