How to Kill Algae in a Freshwater Pond


A freshwater pond filled with algae becomes visually unappealing and can pose a health hazard to the fish if left to flourish. During winter months, the cold temperature of the pond water inhibits the growth and reproduction of algae. When spring arrives and the water of the pond begins to warm, the algae becomes more prolific. Barley straw breaks down in water to produce a substance that is believed to interfere with the growth of algae, according to The Ohio State University. The use of barley straw is safe around fish, mammals and waterfowl.

Step 1

Begin applying barley straw to the freshwater pond in April, before the weather warms, to control algae growth.

Step 2

Break up the bale of barley straw and apply it at a ratio of 1/4 lbs. per square yard of pond space. Place the barley straw loosely into a mesh bag. Place a rock or a brick into the bag to weight it down to ensure that it anchors on the bottom of the pond.

Step 3

Attach a rope to the end of the nylon mesh bag to tie off outside of the pond and for retrieval.

Step 4

Lower the mesh bag into a shallow spot in the pond. Space multiple bags at different shallow areas around the pond.

Step 5

Keep the mesh bags in water that is no deeper than 6 feet, according to The Ohio State University, or they will have little affect on the algae growth.

Step 6

Replace old, decomposed barley straw in the bag in mid-July. Apply new barley straw one last time in October.

Tips and Warnings

  • Barley hay or green barley will encourage the growth of algae by producing nitrogen and phosphorus during decomposition. The abundance of algae grows and flourishes in warm, shallow water.

Things You'll Need

  • Barley straw
  • Nylon mesh bags
  • Rope
  • Rock or brick


  • The Ohio State University: Algae Control with Barley Straw
  • The Ohio State University: Planktonic Algae in Ponds
  • Aqua Botanic: Pond Algae Control With Barley Straw

Who Can Help

  • Purdue University: Barley Straw for Algae Control
Keywords: algae pond control, algae control, algae freshwater control, barley algae control

About this Author

Kimberly Sharpe is a freelance writer with a diverse background. She has worked as a Web writer for the past four years. She writes extensively for Associated Content where she is both a featured home improvement contributor (with special emphasis on gardening) and a parenting contributor. She also writes for Helium. She has worked professionally in the animal care and gardening fields.