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Rating depth structure for smallmouth bass.
Recent public catches load as you reach this section.
7 km of the Union River navigation corridor, with channel depths from USACE hydrographic survey. The river tops out around 24 ft. The depth chart comes from U.S. Army Corps of Engineers bathymetric survey data, so the contours are survey-derived rather than computer-modeled. What follows comes from the same scoring engine that paints the spots above.
Drawn out, this is 1,944 acres of water rimmed by 10.5 miles of bank. The shoreline is moderately structured (index 1.7) — enough points and pockets to pattern. 87% of the surface is littoral (under ~15 ft) — cover, weeds and forage water. Call it 4.5 mi long by 1 mi wide at the broadest reach. Closest neighbour on DepthScout: Morgan Bay, 5 mi southwest of here.
The spring pattern is a shallow one: smallmouth bass in 3 to 12 ft. As the season builds they drop to 7 to 24 ft, wintering in 7 to 24 ft. Top water on the chart: Current seam (mile 0.2), a current seam in the 23 ft range, prime in summer. Time it for early morning and the evening. Summer baits: a drop shot (goby/minnow) or a ned rig gets it done.
Depth note: when a documented seasonal range extends below this chart, the table shows the deepest mapped working water, not a verified holding depth.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 3 to 12 ft | dawn & dusk | Slackwater eddy (mile 3.8) (9 ft) | Ned rig, Tube jig |
| Summer | 7 to 24 ft chart-limited; documented 10 to 30 ft | dawn & dusk | Current seam (mile 0.2) (23 ft) | Drop shot (goby/minnow), Ned rig |
| Fall | 7 to 24 ft chart-limited; documented 8 to 25 ft | midday & dawn | Current seam (mile 0.2) (23 ft) | Jerkbait, Blade bait |
| Winter | 7 to 24 ft chart-limited; documented 20 to 45 ft | midday | Current seam (mile 0.2) (23 ft) | Blade bait, Hair jig |
Come spring, look for chain pickerel tight to the bank in 2 to 10 ft. Expect a summer slide to 3 to 15 ft, then a winter hold in 5 to 18 ft. Start at Slackwater eddy (mile 3.8). It's an eddy pocket holding about 9 ft of water and rates good come winter. Prime time lands in early morning and the evening. A weedless spoon + trailer or a buzzbait is the honest summer answer here.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 2 to 10 ft | midday & dawn | open water | Inline spinner (silver), Small spoon (red/white) |
| Summer | 3 to 15 ft | dawn & dusk | open water | Weedless spoon + trailer, Buzzbait |
| Fall | 4 to 15 ft | midday & dawn | open water | Jerkbait along weed edges, Spinnerbait |
| Winter | 5 to 18 ft | dawn | Slackwater eddy (mile 3.8) (9 ft) | Jigging spoon (through ice) |
Spring puts white perch in skinny water — 4 to 15 ft is the zone. Warm water sends them out to 7 to 24 ft; cold water stacks them in 7 to 24 ft. Slackwater eddy (mile 3.8) is the standout, an eddy pocket at roughly 9 ft, rated prime for summer white perch. Plan around early morning in the warm months. A small spinner rig drifted or a 1/8 oz jigging spoon covers the summer program.
Depth note: when a documented seasonal range extends below this chart, the table shows the deepest mapped working water, not a verified holding depth.
| Season | Depth | Best window | Start at | Go-to baits |
|---|---|---|---|---|
| Spring | 4 to 15 ft | dusk | Outside-bend hole (mile 2.0) (16 ft) | Small jig + curly tail, Inline spinner (silver) |
| Summer | 7 to 24 ft chart-limited; documented 15 to 40 ft | dawn | Slackwater eddy (mile 3.8) (9 ft) | Small spinner rig drifted, 1/8 oz jigging spoon |
| Fall | 7 to 24 ft chart-limited; documented 15 to 45 ft | midday | Slackwater eddy (mile 3.8) (9 ft) | Jigging spoon (small), Blade bait |
| Winter | 7 to 24 ft chart-limited; documented 20 to 50 ft | dusk | Slackwater eddy (mile 3.8) (9 ft) | Small rattle spoon, Tungsten + spikes |
Count 3 structure marks on this chart. The deepest, Current seam (mile 0.2), sits near 23 ft.
Access data: Maine GeoLibrary — Boat Launches (Maine IF&W / DACF). Confirm conditions and fees locally before you launch.
Season dates, license requirements, and size and bag limits for Maine waters are set by the Maine IFW — and special regulations can apply to Union River specifically, so confirm the current rules before you fish.
Check the official Maine fishing regulations →
Union River is about 24 ft (7 m) deep at its deepest point. The depth chart comes from U.S. Army Corps of Engineers bathymetric survey data, so the contours are survey-derived rather than computer-modeled.
Anglers target smallmouth bass, chain pickerel, white perch on Union River. This isn't a survey of the water — none is published for it — but an informed estimate from the species common to the region, narrowed by this water's depth, size and each species' range.
Current seam (mile 0.2) is the top-rated area: a current seam in about 23 ft of water that rates prime for smallmouth bass in summer. Every other rated spot, per species and season, is on the map above.
For smallmouth bass, the summer bite is best in early morning and the evening. Each species page section below lists the seasonal windows, and the map shows a live NOW badge when you're inside one.
Fishing on Union River is regulated by the Maine IFW. Check the official Maine regulations for current license requirements, season dates, and size and bag limits — special regulations can apply to this specific water.
Morgan Bay 5 mi · Lower Patten Pond 6 mi · Eastern Bay 8 mi · Noyes Pond 8 mi · Branch Lake 9 mi · Blue Hill Harbor 10 mi · Green Lake 10 mi · Lake Wood 10 mi · Sorrento Harbor 12 mi · Long Pond 13 mi · Beech Hill Pond 13 mi · Eastern Point Harbor 13 mi
See how Union River stacks up: best smallmouth bass lakes in Maine · best chain pickerel lakes in Maine · best white perch lakes in Maine
Browse all Maine fishing maps. See every water on DepthScout. Bathymetry credit: U.S. Army Corps of Engineers. How we build these maps. Fish here with a sonar unit that logs? Send us your depth data and we'll improve this chart, credited to you. For fishing guidance only, never navigation.