North Avenue Beach has the cleanest water-test record on Chicago’s lakefront: since 2021, just 1.4 percent of its lab tests came back at or above the Park District’s swim-advisory action level — 8 of 558 — with Foster (1.6 percent) and Oak Street (1.8 percent) close behind. At the other end sits 63rd Street, where 10.3 percent of tests hit that level, seven times North Avenue’s share. This page ranks all 17 lakefront beaches the city tests, cleanest record first, from their 9,524 lab results in the city’s own beach file since 2021. One precision note up front: these are test results, not posted advisories — a test at or above the action level is the trigger the Park District’s yellow-flag threshold describes, and the counting details live in the full analysis. Water quality moves day to day; this record spans the 2021 seasons through the partial 2026 season, not any single morning, and this page takes no position on where anyone should swim today.
1. North Avenue — 1.4 percent of tests at advisory level
North Avenue logged 8 advisory-level results in 558 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
2. Foster — 1.6 percent of tests at advisory level
Foster logged 9 advisory-level results in 560 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
3. Oak Street — 1.8 percent of tests at advisory level
Oak Street logged 10 advisory-level results in 557 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
4. Osterman — 1.9 percent of tests at advisory level
Osterman logged 11 advisory-level results in 566 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
5. 57th Street — 2.7 percent of tests at advisory level
57th Street logged 15 advisory-level results in 558 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
6. Leone — 3.4 percent of tests at advisory level
Leone logged 19 advisory-level results in 565 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
7. Oakwood — 3.4 percent of tests at advisory level
Oakwood logged 19 advisory-level results in 552 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
8. 12th Street — 3.6 percent of tests at advisory level
12th Street logged 20 advisory-level results in 560 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
9. Hartigan (Albion) — 3.9 percent of tests at advisory level
Hartigan (Albion) logged 22 advisory-level results in 565 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
10. South Shore — 4.8 percent of tests at advisory level
South Shore logged 27 advisory-level results in 565 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
11. Rainbow — 4.9 percent of tests at advisory level
Rainbow logged 28 advisory-level results in 566 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
12. Marion Mahony Griffin (Jarvis) — 5.7 percent of tests at advisory level
Marion Mahony Griffin (Jarvis) logged 32 advisory-level results in 564 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
13. Ohio Street — 8.2 percent of tests at advisory level
Ohio Street logged 46 advisory-level results in 563 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
14. Margaret T Burroughs (31st) — 8.7 percent of tests at advisory level
Margaret T Burroughs (31st) logged 48 advisory-level results in 551 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
15. Calumet — 8.8 percent of tests at advisory level
Calumet logged 49 advisory-level results in 558 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
16. Montrose — 9.4 percent of tests at advisory level
Montrose logged 53 advisory-level results in 561 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
17. 63rd Street — 10.3 percent of tests at advisory level
63rd Street logged 57 advisory-level results in 555 tests since 2021. The share is that beach’s full record from the city’s lab file, 2021 through the partial 2026 season, and closely spaced beaches can swap places as new tests land.
And one inland lagoon, counted apart
Humboldt is the one beach in the file that is not on Lake Michigan — it is an inland lagoon, and the parent analysis never averages it into the lakefront. Counted apart: 41 advisory-level results in 240 tests since 2021, 17.1 percent — a higher share than any lakefront beach, on a different body of water with about half the testing volume.
Questions these numbers can answer
Which Chicago beach has the cleanest water-test record? North Avenue Beach: 1.4 percent of its lab tests since 2021 came back at or above the advisory action level, the lowest share on the lakefront, with Foster and Oak Street next. A test-share record is not a general cleanliness verdict — it measures one threshold on one test.
Which Chicago beach has the most advisory-level test results? 63rd Street, where 10.3 percent of tests since 2021 came back at or above the advisory level — about one test in ten, and seven times the share at North Avenue. Montrose (9.4 percent) and Calumet (8.8 percent) follow.
What counts as an advisory-level test? A rapid DNA (qPCR) result at or above 1,000 CCE per 100 mL — the Park District’s own yellow swim-advisory action level. The older culture test uses a different threshold and is a different measurement; the two are never mixed in these counts.
Where these numbers come from
The City of Chicago’s Beach Lab Data file (2ivx-z93u): 9,524 rapid-test results at the 17 lakefront beaches from samples taken January 2021 through mid-July 2026, 473 of them at or above the advisory action level — 5.0 percent of lakefront tests. Humboldt’s 240 tests are counted apart from those totals, per the parent’s own rule. Each beach’s share is its own tests only. The season-by-season arc, the threshold’s meaning, and every caveat: The Yellow Flag Flies 7 Times as Often at One Chicago Beach as at Another.
Computed by KCM Desk from records current to July 18, 2026. If you spot an error, corrections come first.