Here's a problem to solve: An increase in phosphate levels in a lake increases the population of algae in the lake. Increased algae blocks sunlight into the lake and results in a decrease in dissolved oxygen in the lake's water. Which of the following should be expected as a result?

Among the 4 following options, which is the correct answer?

- A: Plant populations in the lake increase.
 
- B: More predatory birds feed on lake animals.
 
- C: Phosphate levels in the lake decrease.
 
- D: Fish populations in the lake decline.
 