Jan Doggen's answer identifies some sources that tell a bit more about Boomy itself, so I'd like to address overall what a boom actually is in this context, and make an educated guess about the purpose of Boomy.
A boom, in this context, is a large floating device intended to surround or block an area of water, keeping surface contaminants either in or out (depending on the application). Most commonly they are used in isolating oil spills, or protecting sensitive locations from oil. Oil floats on water, and a floating boom creates a surface barrier which effectively blocks the oil from spreading. This page from the National Oceanic and Atmospheric Administration (NOAA), a division of the United States government, explains the various types of booms commonly used in environmental cleanup.
Some excerpts from the page:
Booms are floating, physical barriers to oil, made of plastic, metal, or other materials, which slow the spread of oil and keep it contained.
There are three main types of boom. Hard boom is like a floating piece of plastic that has a cylindrical float at the top and is weighted at the bottom so that it has a "skirt" under the water. If the currents or winds are not too strong, booms can also be used to make the oil go in a different direction (this is called "deflection booming"). Sorbent boom looks like a long sausage made out of a material that absorbs oil. If you were to take the inside of a disposable diaper out and roll it into strips, it would act much like a sorbent boom. Sorbent booms don't have the "skirt" that hard booms have, so they can't contain oil for very long. Fire boom is not used very much. It looks like metal plates with a floating metal cylinder at the top and thin metal plates that make the "skirt" in the water. This type of boom is made to contain oil long enough that it can be lit on fire and burned up.
With that in mind, and considering the context of Boomy McBoomFace having something to do with the Pacific garbage patch, I think it is safe to theorize that Boomy is being designed to help collect garbage floating at the surface in a similar manner to how the booms described above collect/block oil.