Brzak was a human-based B.O.W. created by the C-Virus. It was encountered by Leon and Helena within the depths of the ancient Catacombs that lie under the Tall Oaks Church. It's name is derived from the Serbian word for "Rapids".
According to its file, the Brzak was one of the Family's experiments with the C-Virus. The Brzak was used by the Family to dispose of dead test subjects, due to its predatory instinct to hunt down and eat anything that moves in the water. Before the Tall Oaks Bioterror Incident, Derek C. Simmons ordered his men to release the Brzak from its aquarium should anyone break into the Family's hideout.
The Brzak was first encountered when Leon and Helena tried to escape the underground facility under the church. They quickly saw a disturbance in the water, noticing the large fin splashing around. The B.O.W was trapped behind underwater rubble, allowing Leon and Helena to escape. The Brzak eventually manages to sneak up on Helena and pull her underwater, only escaping after a fierce struggle.
After the duo are trapped in underwater ruins, the Brzak stalks them as they swim for air. It catches Helena and Leon is forced to climb up onto its back to help her. They gouge out the creature's eyes, successfully forcing it away. Leon encounters it again while swimming to safety and must narrowly avoid its attempts to pull him underwater.
The Brzak swims after the two when they fall into an underground waterfall and they are forced to shoot its mouth to keep it at bay. The Brzak was killed when Leon (or Helena) shot an explosive barrel flying above them, sending shockwaves and shrapnel into the creature's open mouth.