Algae are photosynthetic organisms that show up in bunkers when the surface stays damp, the sand packs tight and faces don’t get disturbed. Their presence darkens the sand and creates a hard crust that limits water infiltration and affects playability. The good news is you can solve algae issues by managing moisture near the surface through sand disturbance, increasing sand depth and improving drainage. Let’s start by taking a closer look at some of the reasons why bunkers become algae-prone.
Fine/angular sands pack tightly. Sand that is chosen because it delivers firm conditions may also reduce infiltration at the surface, resulting in thin films of moisture that persist after rain, irrigation or heavy dew. This is the exact microhabitat where algae thrive. The brilliant white color of many premium sands unfortunately also makes contamination more visible.
Undisturbed faces form sealed crusts. When faces are left smooth rather than regularly disturbed – i.e., the “Aussie method” – the sand forms a superficial crust that stays slightly damp. This can be desirable for keeping balls from getting stuck in bunker faces, but it also encourages a thin algal mat to form and reinforce itself over time. Breaking that mat is essential to eliminating an algae issue.
Fine particles and organic material clog the sand. Silt, clay and organic debris like leaf litter and grass clippings accumulate in bunker sand and progressively reduce infiltration, keeping the top inch wetter for longer. Minimizing very fine particles is an important part of sand selection and managing contamination is crucial for extending sand life and reducing the risk of algae formation.
Liner and drainage systems can create a perched water table. Porous-aggregate bunker liners can cause water to perch in the sand and stay wetter than desired. To manage this issue, some courses intentionally leave gaps in the liner, use a different liner material, or skip liners altogether. You want to ensure a free-draining path for water to flow out of the sand layer. More information on this topic is provided in the Green Section Record article “A Guide for Selecting Bunker Liners.”
Now that we understand some of the reasons why algae form in bunker sand, we can talk about practical solutions to this problem.
Use lab tests to help determine sand depth. An accredited lab’s moisture column test will allow you to set bunker sand depths that ensure proper drainage for the sand you have selected. You want to determine the depth at which saturated sand dries to 15% moisture content after 48 hours. Then, install that depth plus an additional inch on bunker floors. For example, if it takes 6 inches of sand to achieve 15% moisture content after 48 hours, put 7 inches of sand in the bunker floor. This keeps the top layer of sand drier between rain or irrigation events and reduces algae pressure. For more information on bunker sand depth, review the Green Section Record article “Deep Thoughts About Bunker Sand Depth.”
Break the mat and keep faces disturbed. Scarify or spring-tine rake faces at least once per week during warm and/or wet weather and when irrigation is applied routinely. Physically remove any cohesive algae mats before they re-bond. This disruption restores infiltration and speeds surface drying. If you are using the Aussie method and struggling with algae in bunker sand, you may benefit from rethinking this approach and raking the faces more routinely.
Control contamination. Keep debris out by using a blower before raking, minimizing exposed soil edges and diverting runoff away from bunkers. You should also monitor fine material accumulation over time. Many courses add sand annually to bunkers to improve aesthetics, playability and to dry the surface. However, if the sand below this new layer is heavily contaminated, “topping off” will only offer temporary improvement and sand replacement is likely necessary. The Green Section Record article “Monitoring Sand Contamination in Bunkers” has helpful information on how to know when it might be time for sand replacement.
Choose the right sand. When selecting or replacing bunker sand, prioritize a gradation with minimal very-fine sand, silt and clay particles and infiltration exceeding 30 inches per hour. Particle size distribution and sand shape are the two biggest drivers of drainage, crusting potential and long-term playability. The Green Section Record article “A Guide To Selecting the Right Bunker Sand for Your Course” provides more information on this topic.
Verify drainage and tweak liner details. If you notice that bunker sand is holding excessive moisture, run some water through your bunker drainage to make sure it is functioning properly and repair or flush the lines if needed. If you’re planning a bunker renovation that will include a porous-aggregate liner, discuss options with your vendor to avoid creating a perched water table.
Set sand depth by testing, not by feel. Get a moisture column test on your sand and adopt the 15% moisture at 48 hours depth plus 1 extra inch rule, especially for bunker floors. This is the most reliable lever for keeping the top layer of sand dry.
The bottom line is that algae is a symptom of persistent near-surface moisture. Fix the characteristics that you can control: Select sand that drains and dries, disturb sand on the slopes and faces to mitigate sealing, keep the sand as clean as possible, and use bunker liner materials or designs that do not perch water. There may still be instances where algae develop despite these practices – e.g., on north-facing slopes, shaded bunkers and in wet, humid environments – but these situations are out of your control and increased raking and more-frequent sand addition or replacement will be necessary if the presence of algae cannot be tolerated by golfers.
West Region Agronomists:
Brian Whitlark, regional director, West Region – bwhitlark@usga.org
Ross Niewola, agronomist – rniewola@usga.org