(Radio Iowa) – The dead zone in the Gulf of Mexico is smaller this year, primarily because the Mississippi River basin is so dry, the waterway is moving less water and carrying fewer nutrients from states like Iowa. Nutrient pollution, in the form of nitrogen and phosphorous, is the main cause of low oxygen levels that threaten marine life in the Gulf.

In Iowa, those nutrients commonly come from excess farm fertilizer that washes into waterways. Iowa Secretary of Agriculture Mike Naig says federal infrastructure funding will help states scale up conservation efforts. Long-term studies show the rate of surplus fertilizer applied to the land has slowed in recent years.

This summer’s dead zone covers just over three-thousand square miles. That’s among the smallest it’s measured since 1985, but over a five-year average, the hypoxic zone is still more than twice as large as the goal set by river states and federal regulators.