Understanding Oxygen Level Impact on Bass

Oxygen level, particularly in warm stagnant water or deep summer water, negatively impacts bass metabolism as oxygen is required to generate energy. Oxygen level, also called dissolved oxygen or oxygen saturation, is produced by aquatic plants using the sun for photosynthesis, thus created in shallow water then mixed with deeper water. Oxygen is also introduced to surface water through atmospheric exchange with the water and air. Water’s capacity to hold oxygen is impacted primarily by water temperature, with colder water having a higher maximum saturated dissolved oxygen than warm water. 

Why is understanding Oxygen Level Impact on Bass Important?

It is important to understanding oxygen level impact on bass to:   

  • Find Fish: Bass leave locations with very low dissolved oxygen levels which could impact late summer largemouth bass in shallow, grassy, wind protected water or smallmouth that won’t go below the thermocline (low oxygen) in the summer.
Understanding oxygen Level Impact on Bass
  • Negative Impact Scenarios: Low oxygen levels can result from:
    • Decaying Grass: Particularly, decaying grass that results from:
      1. Warm Water: High water temperatures reduce that amount of oxygen the water can hold.
        and 
      2. Stagnant Water: [Figure 1 and 2]  Decoying grass from bacteria resulting from the warm water.  This scenario typically takes place:
        • Fall: In the fall when there is less sunlight but warm air in protected locations.
        • Murky Water – Cloudy Days: It can also occur in murky water combined with long stretches of cloudy days. 
        • Heavy Floating/Matted Grass: Heavy surface grass blocks the sun and light winds killing the grass under the canopy.
        • Algae Bloom: [Figure 3] A sustained algae bloom can block sun to underlying grass especially if there are brown streaks.
    • Thermoclines: [Figure 4] .
      • Reduced oxygen below the thermocline.
  • Early Dawn Bass Position: Some suggest that bass that use grass cover will go outside the grass line during the evening when the oxygen level is lowest and on cloudy mornings stay there longer than sunny mornings.
  • Positive Impact Scenarios: Possibly, in some scenarios:
    • Green Grass: In the fall, when grass is dying, some suggest bass will hold to greener grass possibly partially as during the day they produce oxygen.
    • Oxygen Rich Environment: Saturated oxygen levels are common at river mouths, choppy water, current, below dams, and after rain.  
Figure 1: Decaying Grass & Low Oxygen Water
Figure 2: Decaying Grass & Low Oxygen Water
Figure 3: Algae Bloom
Figure 4: Thermocline at 22 Feet
Additional Considerations
  • Live Wells: Some pros put ice in the live wells presumably to reduce the water temperature which increases the oxygen level.
It's About the ALLURE™

Fishing Deep Lures
When fishing above the thermocline. 

Fishing Shallow Lures
When fishing shallow, avoid locations with low oxygen levels.

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