From the Super Mario Wiki
Proximity Mines are explosive objects from Donkey Kong Country: Tropical Freeze. They are scattered throughout the underwater portions of Irate Eight, a level in Sea Breeze Cove, but a few can also be exposed in Shoal Atoll.
Approaching a Proximity Mine will make it flash and, eventually, trigger its explosion. The explosion can be avoided if the Kongs distance enough from the mine. Should it explode, however, four pieces of shrapnel will get flung in diagonal directions, damaging the Kongs and even enemies upon impact with them. This defensive pattern was previously seen at Puftups from Donkey Kong Country 2: Diddy's Kong Quest. Proximity Mines can explode prematurely if the Kongs head into them as they flash, or if they are hit by the shrapnel of another mine, sometimes creating a chain explosion between several mines.
Proximity Mines are usually stationary or moving on set paths, as it can be seen at the beginning of the stage and in the second Squiddicus chase sequence. Several mines are driven by the water current before the first checkpoint. In Shoal Atoll, three Proximity Mines appear from the ceiling by collecting the middle ring of reeling bananas in the area after the green chest.