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Josh Morrisey

Manito Park’s Mirror Pond to Be Rehabilitated

Josh Morrisey, City of Spokane Parks & Recreation, Marketing Assistant, 509.625.6236

Thursday, September 12, 2019 at 3:34 p.m.

Manito Park’s Mirror Pond to Be Rehabilitated

Updated June 23, 2020

This project is now complete.

In recent years, Spokane residents may have noticed Manito Park’s Mirror Pond has been looking… a little green, to say the least. The culprit? Planktonic algae.

Buildup of broken down organic material on the bottom of the pond has loaded the water with both nitrogen and phosphorous, which are great foods for algae (one pound of phosphorus can support over 500 pounds of algae). The pond is also shallow and there is not enough water above the pond floor to filter out light, which also aids algae blooms. Algae is not harmful to pond ecosystems in small amounts, but large blooms not only cloud the water, they remove oxygen from the water, harming wildlife.

The restoration project aims to solve this algae buildup problem without the use of toxic chemicals with six important steps.

  1. Safely removing wildlife from the pond in accordance with the Washington State Department of Fish and Wildlife
  2. Dredging the pond to remove sediment
  3. Deepening the pond to increase pond volume and reduce algae bloom
  4. Installing treatment wetland to filter out phosphorous and nitrogen before it rebuilds
  5. Reintroducing water and indigenous wildlife to the pond
  6. Implementing a yearly pond management plan to keep healthy after the rehabilitation

It’s important to note that a healthy pond is not completely free of algae, but has moderate enough amounts to benefit the ecosystem of the pond without blooming to the point of removing too much oxygen from the water. So, will Mirror Pond be crystal-clear or bright blue after the rehabilitation project? Not quite, but the difference will be dramatic. Most importantly, the pond will be healthy again.

The project is expected to start in late fall 2019 and be completed by spring 2020.

Big thanks to the Friends of Manito for their financial support of this project.

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