The researchers studied a lake in South Korea to understand its food chain and overall health. They looked at the water quality, types of organisms living there, and how much energy was being passed around. The lake had too many nutrients, leading to poor health. Most of the energy flow happened at the bottom of the food chain, with small plants being eaten by many different animals. The top predator in the lake was a type of catfish. This study shows how nutrients can affect the way energy moves through a lake ecosystem.