A mobile HEB and TEP mitigation device includes a mobile body capable of movement within or upon a body of water. Located within the mobile body is a hydrodynamic separation system which includes a water inlet, a hydrodynamic separation unit and a collection tank. The hydrodynamic separation unit includes two outputs, one for a clean stream output line containing clean water and arranged to re-circulate the clean water, and another for a concentrate stream output line, the concentrate stream output line configured to place concentrated water containing potentially harmful bio-organic materials into the collection tank. Also included on the mobile body is a power source and an engine/steering unit, wherein the steering portion of the engine/steering unit provides a capacity to move the mobile body in an intended direction. The mitigation device may also be used as an embedded part of an on-shore arrangement.

A containment system for recovering hydrocarbon fluid from a leaking device comprising a wall extending from a base level to a first level for surrounding the leaking device, and a dome situated above the wall and forming a cavity for accumulating hydrocarbon fluid. The dome comprises an upper output opening for extracting the hydrocarbon fluid. The containment system further comprises a lower output opening extending up to a dome level. The wall and the dome are independent members so as the wall can be landed on the seafloor before the dome is installed.