Simplify the following text for a Grade 6 native English-speaking person.
Original: Naini Lake is deep , but , according to experts , the level of oxygen in the hypolimnic layer ( the bottom , colder , stagnant , and constant temperature layer ) is much lower than is required to sustain fish -- and this is mostly due to pollution , which includes illegal dumping of garbage .
Simplified: Naini Lake has too low a level of oxygen in the bottom layer to sustain fish . This is mostly due to pollution , which includes illegal dumping of garbage .