The only large publicly available repository of underwater marine debris images is the Deep-sea Debris Database (https://www.godac.jamstec.go.jp/dsdebris), curated by the Japan Agency of Marine Earth Science and Technology (JAMSTEC). Available data contains images of marine debris and various types of marine plants and animals captured in underwater surveys by remotely operated vehicles (ROVs), mainly in the sea of Japan.
Researchers in Croatia and the Netherlands have developed Seaclear Marine Debris Dataset, the first publicly available underwater marine debris dataset in shallow-water environments, annotated for instance segmentation and object detection tasks. Data collection was performed by deploying camera-equipped Remote Operated Vehicles (ROVs) at different sites. A BlueROV2 was equipped with two cameras, a Bluerobotics Low-Light HD Camera and a Paralenz Vaquita, while the SST Mini-Tortuga ROV was equipped with a Smart Security SIP-E323CV camera.
Research paper at: NIH National Library of Medicine