An ichthyologist observes a population of 1,200 fish in a lake. Due to pollution, the population decreases by 18% annually. What will the population be after one year? - Parker Core Knowledge

Understanding the Context

The Science Behind the Numbers

An ichthyologist tracks a survey showing 1,200 fish in a specific lake. Annual pollution compression, caused by industrial runoff, chemical contamination, or nutrient overload, triggers a consistent yearly drop of 18%. This figure reflects real-world data on population stress in freshwater systems impacted by human activity.

Mathematically, a population decreasing by 18% means maintaining 82% of the original count each year. Applying this to 1,200 gives a post-year calculation:
1,200 × (1 – 0.18) = 1,200 × 0.82 = 984 fish.

The resulting 984 fish reflect the measurable impact—without ongoing intervention, such annual losses accumulate, reshaping lake biodiversity.

Key Insights

Why This Matters to Communities Across the U.S.

This shrinking population isn’t a niche concern. Across rural and suburban waterways, fish are central to recreation, food security, and environmental health. For anglers, conservationists, and families enjoying lakes, a declining 18% annual drop sparks real discussion about pollution sources, water treatment investments, and ecosystem resilience.

Current conversations focus on policy changes, community clean-up initiatives, and ongoing scientific monitoring—especially as pollution connections grow clearer through changing fish counts like this one.

How Pollution Drives This Decline

Fish rely on clean water, stable temperatures, and intact habitats. Pollution introduces toxins, depletes oxygen, and disrupts breeding cycles. Over time, repeated exposure weakens populations. The 18% annual decline observed reflects compounding stress—chemical contamination alters water chemistry, while sediment runoff smothers spawning grounds, reducing survival odds.

Final Thoughts

Tracking numbers—such as tracking