What is a Watershed?

When we talk about restoring Easter Lake we talk a lot about it’s watershed. But what is a watershed and why does it matter?

If we can understand the location of the Easter Lake watershed, how it functions, and the factors that influence the quality of water within it, we can learn what actions are needed to be taken to restore Easter Lake and protect it into the future.

A watershed is an area of land in which all streams and rainfall drains to a common outlet like the outflow of a reservoir, the mouth of a river, or any point along a stream channel. The terms drainage basin, river basin, and catchment are also used to reference watersheds.

A watershed boundary is defined by the ridges of the area that topographically appears to drain water to a common point. A watershed can be as small as the area of two adjoining hillsides or it can be a larger area in which all the water drains to a single point like a lake.

Understanding watersheds is critical to understanding stream flow, water quality, and how to effectively manage water resources in sustainable ways. Anything happening in the land-area of a watershed affects the quantity and quality of water in that watershed.

No matter where you are, if you are standing on the ground on planet Earth you are in a watershed.

The Pieces of a Watershed Puzzle

As can be seen in this photo, water runs off the mountain sides into Monte Cristo Creek and into Blue Lakes. The ridges of the mountains clearly define the boundaries of the watershed that drains to Blue Lakes.

Here we can see how small watersheds fit into larger watershed. At the smalles level, 2 adjoining hillsides for a watershed. As water and streams flow downhill it combines with other streams that are part of different watersheds together forming larger watershed. In the above photo, each colored outline represents a watershed.

Components of a Watershed

A watershed consists of surface water including streams, lakes, wetlands, reservoirs and groundwater. However, the quality and quantity of stream and groundwater flow in a watershed is dependent on geology, soils, topography, land use, and climate.


How water flows throughout a watershed depends on the land – how it’s shaped, what it’s made of, and how the land is used. What direction is the water flowing? Is the water flowing slowly through thick grasslands and temporarily stored in a wetland? Is rainwater infiltrating through the soil recharging groundwater aquifers? How is this water running across an agricultural field? Is water rapidly flowing off buildings and parking lots into storm drains? Read more below to learn how different components of the land affect water flow.


In Iowa, healthy soils function like a sponge helping to naturally infiltrate and percolate water into the soil profile. This process helps store water, recharges aquifers, and naturally filters the water.  When damaged through compaction or over use, soil loses its structure and ability to store water leading to increased surface water runoff.

Did you know across Iowa there over 450 soil subtypes? Each soil type has different characteristics affecting how water flows through them. Soils such as clay are very compact poorly infiltrating and storing water while others can store lots of water or are easily eroded by runoff. Soil types help inform us of how water will flow and help us to strategically place development and conservation practices and manage resources.


Historically Iowa was covered by tallgrass prairie and woodlands. The prairie, made up of dense grass and forbes with deep fibrous roots helped to slow down and store water in the soil naturally filtering water. As vegetation changes or is removed, there is an impact to how water will flow and the quality of that water, overall altering the watershed.

Think about a grassland or prairie – is there any exposed soil? Now think about a construction site or agricultural field in winter or early spring, how much soil is exposed? The amount of exposed soil has a direct impact on the amount of erosion that will occur on that landscape. Unless treated, exposed soil is eroded and carried away by water impacting water quality and land within the watershed.

Land Use

How land is used may have the biggest impact on water quality and how water flows in a watershed. In places where Iowa prairie is still intact, native vegetation ensures healthy soils that can store and filter large amounts water. In densely urban areas, much of the landscape is covered with buildings, streets, and parking lots. These impervious surfaces do not allow for natural infiltration and rapidly send water to streams during rainstorms causing erosion and even flooding. In agricultural areas, compacted soils without vegetative cover easily erode into waterways and decreases soil health.

Within a watershed, any land use change has an effect. For example, if a natural wetland is removed, it must be understood the water that was once stored there has to go somewhere else. If soil is compacted, the soil loses its ability to store water causing that water to runoff somewhere else as well.


A watershed is a system of flowing water so it’s no surprise that climate and precipitation have a large impact. The amount, type, and frequency of precipitation dictates stream flow rates and how soils and vegetation will respond to rain events.

In urban and rural areas, land use changes have severely changed our landscape thus changing our watersheds’ hydrology – the movement of water. As watersheds become urbanized or soils are compacted and natural wetlands and vegetation are removed, water enters streams more rapidly. These rapid and flashy flows carry pollutants, cause erosion and even flooding in some cases. Recognizing the effects of land use change and linking that to local climate and precipitation data, can inform us of risks for flooding and erosion, and can help determine what actions we can take to address these problems to protect our farmland, cities, natural resources and water quality.

The Easter Lake Watershed

The Easter Lake watershed fairly small at 6,380 acres or nearly 10 square miles. Easter Lake eventually drains into the Des Moines River which flows into Lake Red Rock then continues all the way to the Mississippi River which drains into the Gulf of Mexico. The Easter Lake Watershed is part of the greater Mississippi watershed.

The Easter Lake watershed starts at the Des Moines International Airport and extends east to Easter Lake. Three main streams feed Easter Lake including Yeader Creek and two unnamed tributaries. Land use in the watershed is 45% urban, 25% grassland, 14% forest, 13% cropland and 3% other.

On the map above the red line represents the Easter Lake Watershed.  If you live in the watershed you are eligible for special cost-share and financial incentive for rainscaping practices.


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