conditions glossary
What is lake stratification, and what does turnover do to the fishing?
In summer many lakes split into layers and the water below the stratification level loses oxygen; fall cooling mixes them again and sends bass deep.
Many lakes stratify at 6 to 20 feet in summer. There is no oxygen or fish below the stratification level, so the fishable water is the oxygenated layer above it. As fall progresses and the water cools to the low-to-mid 50s, bass return to deep water as the lake mixes.
That mixing event — turnover — is why post-turnover fishing shifts deep. baromoon watches for it and flags the lake state in the report.
See it in the report
Sources (quoted verbatim)
“Along with temperature, dissolved oxygen is a major factor determining where to find bass during summer. Many Iowa lakes stratify at depths from 6 to 20 feet. There is no oxygen or fish below the stratification level.” — Iowa DNR — Largemouth bass · T2 (checked 2026-09-29)
“As fall progresses and water temperature cools to the low to mid-50's, bass will return to deep waters.” — Iowa DNR — Largemouth bass · T2 (checked 2026-09-29)