The conversion of wetlands to farmland has generally made nearby streams and rivers dirtier , flashier (more sudden floods), and less stable over time.

Quick Scoop

When you drain or plow a wetland, you don’t just change the land — you change how every rainstorm moves through streams and rivers downstream.

1. Loss of nature’s “filter”

Wetlands act like giant natural filters and sponges around streams and rivers.

When they’re converted to cropland:

  • Fertilizers (nitrogen, phosphorus) and pesticides wash straight into streams instead of being trapped and broken down in wetland soils.
  • More nutrients in rivers fuel algal blooms and can lead to low‑oxygen “dead zones” that harm fish and invertebrates.
  • Sediments that wetlands used to trap now move downstream, making water cloudy and smothering fish eggs, mussels, and aquatic plants.

A 2019–2020 style of study on wetland conversion to farming found higher concentrations of nutrients and sediments in water leaving farmed wetlands compared to natural ones.

2. Faster, flashier runoff and flooding

Natural wetlands soak up stormwater, release it slowly, and help spread flood peaks over time.

After drainage and conversion to farmland:

  • Streams receive rainwater much faster, so water levels rise quickly and then drop sharply — “flashy” flows.
  • Floodplains are often cut off or confined by drainage and levees, reducing natural flood storage and increasing downstream flood risk.
  • Tile drains and ditches in farm fields act like express lanes, piping water (and nutrients) rapidly into rivers.

In places like the U.S. Midwest, loss of wetlands plus intensive drainage has been linked to more nutrient‑rich runoff during storms and higher treatment costs for drinking water drawn from rivers.

3. Changes in stream shape and erosion

Because wetlands no longer slow flows or trap sediments, streams and rivers adjust physically.

  • Stronger peak flows erode banks, making channels wider and deeper over time.
  • Sediment from fields and eroding banks can fill in pools and habitat structures that many fish and invertebrates depend on.
  • Some rivers get “straightened” and confined as part of farmland drainage projects, cutting them off from floodplain wetlands.

A classic example along several European and North American lowland rivers is that reclamation of floodplain wetlands for agriculture left channels confined to narrow beds with reduced natural side channels and wetlands.

4. Impacts on water quality and ecosystems

All of this adds up to stressed freshwater ecosystems.

  • Fish and mussels that need clean, cool, oxygen‑rich water struggle as nutrients and sediments increase.
  • Rare wetland and floodplain species disappear when their habitats are drained, plowed, or cut off from the river.
  • Toxic algal blooms can form more easily in nutrient‑rich, slow‑moving reaches and reservoirs, creating risks for drinking water supplies.

For instance, rivers in heavily farmed watersheds where wetlands were largely removed have been listed among the most threatened in the U.S. because of pollution and habitat loss.

5. A quick cause-and-effect chain

You can think of the sequence like this:

  1. Drain/convert wetland to farm
  2. Less water storage and filtering
  3. Faster, nutrient‑ and sediment‑rich runoff
  4. Flashier stream flows and more erosion
  5. Dirtier, more unstable rivers with stressed ecosystems and higher water‑treatment needs

TL;DR: Turning wetlands into farmland removes natural filters and sponges, so more polluted water moves faster into streams and rivers, causing worse water quality, stronger floods, more erosion, and degraded aquatic life.

Information gathered from public forums or data available on the internet and portrayed here.