We used to call them "swamps" but we've learned so much more about Wetlands. 

As Credit Valley Conservation says, they are truly Nature's Multi-Taskers!

Here is an excerpt for their article on Wetlands:

What Wetlands Provide Us..for Free!

• Water filtration – When runoff from roads and fields enters wetlands, they act as filters, removing sediment, absorbing excess nutrients, and break down harmful chemicals.
   
• Flood prevention – Wetlands hold and slowly release water, reducing flood risks. This protects property and significantly cuts flood damage costs. Studies have shown that losing wetlands leads to an increase in flood-related expenses.
   
• Erosion control – Wetland vegetation stabilizes shorelines and prevents erosion. Plant roots trap soils, slow water currents and dampen wave action. Without this natural barrier, controlling erosion is costly and often less effective.
   
• Recharging groundwater – Wetlands are vital to the water cycle. Wetlands collect surface water, replenishing groundwater during dry periods. This is important because we rely on groundwater for agriculture and human consumption.
   
• Supporting wildlife – Wetlands are biodiversity hotspots that provide food, shelter and breeding grounds for many species, including at-risk species, in Ontario. They are essential for the ecological health of agricultural landscapes.
   
• Combating climate change – Conserving and restoring wetlands helps mitigate climate change by keeping carbon trapped in the soil.