How deep is Union Lake?

Union Lake reaches a maximum depth of 110 feet in the Michigan DNR Inland Lake Contours survey. Most of it is far shallower: the survey charts 12 closed depth contours over about 467 acres, and half of that water sits inside the 40 ft line.

Where is the deepest part of Union Lake?

The deepest charted water on Union Lake lies inside the 110 ft contour, toward the middle of the lake. That contour encloses 4.9 acres, 1% of the mapped water, so it is a small target on a small water, the depth chart above gives the contour to line up on.

How much of Union Lake is shallower than 40 feet?

About half. The 40 ft contour encloses 199 acres of the roughly 467 acres inside the outer 5 ft line, so the other half of the water is shallower than 40 feet. The sharpest drop is between 5 and 10 feet, where the mapped water sheds 131 acres.

How accurate is this Union Lake depth map?

The contours come from the Michigan DNR Inland Lake Contours survey, retrieved August 2026 and last rebuilt on August 19, 2026. Depths change over time with water levels and sediment, so treat this map as a planning guide for fishing, and never use it for navigation. Acreages are computed from the published contour geometry, not from a separate area survey, so read them as close approximations.

Michigan lake depth maps

Union Lake depth map

Union Lake in Oakland County, Michigan reaches a depth of 110 feet. Union Lake is charted here across 12 closed depth contours, from the 5 ft line down to 110 ft, enclosing about 467 acres of water. Half of that water lies inside the 40 ft line, and only 4.9 acres lie inside the deepest one. Every contour is on the interactive map below, free and without an account.

Data: Michigan DNR Inland Lake Contours (public record). Contours closed, checked and area-computed by Jordan Carter, founder of GilledIt · page updated August 19, 2026

Union Lake depth chart: 12 depth contours from 5 to 110 ft

Data: Michigan DNR Inland Lake Contours (public record), retrieved August 2026 · depths change over time · not for navigation

Union Lake depth chart data: water enclosed by each contour
Depth contour	Water inside it	Share of mapped water
5 ft	467 acres	100%
10 ft	336 acres	72%
20 ft	267 acres	57%
30 ft	237 acres	51%
40 ft	199 acres	43%
50 ft	149 acres	32%
60 ft	127 acres	27%
70 ft	77 acres	17%
80 ft	51 acres	11%
90 ft	37 acres	8%
100 ft	19 acres	4.1%
110 ft	4.9 acres	1%

Acreages are computed from the closed Michigan DNR Inland Lake Contours contour rings, with islands subtracted. Shares are of the 467 acres inside the outermost charted contour (the 5 ft line), which is the outer edge of the mapped water, several state files carry no 0 ft shoreline line, so this is not the same as a share of the lake's published surface area.

Fishing Union Lake: a stepped drop into deep water

The survey encloses about 467 acres of Union Lake inside its 5 ft contour, and half of that water lies inside the 40 ft line, so the bottom steps down contour by contour into the deep basin rather than shelving flat or plunging all at once. Between 5 and 10 ft the mapped water sheds 131 acres in 5 ft of depth, the sharpest change on the chart, start on that band, because it is where the bottom stops being flat. 4.9 acres, 1% of the mapped water, lie inside the deepest 110 ft contour, toward the middle of the lake. At 110 ft this is two-story water: the basin can stay cold below the summer thermocline while warm-water fish stay up on the 5-to-40 ft ground, and the fish that move between the two do it along the 5–10 ft break at first and last light.

Ice fishing on Union Lake

Deep water like Union Lake freezes later and less evenly than the shallow lakes around it, and the winter bite sets up on the first real break, not out over the 110 ft hole. That edge is the 5–10 ft band on the chart above, where 131 acres of bottom tilt away, and panfish and walleye work up and down it through the day. By late ice the fish push back onto the 5-to-40 ft flat. Check ice thickness locally before you walk out.

Union Lake depth map FAQs

How deep is Union Lake?: Union Lake reaches a maximum depth of 110 feet in the Michigan DNR Inland Lake Contours survey. Most of it is far shallower: the survey charts 12 closed depth contours over about 467 acres, and half of that water sits inside the 40 ft line.
Where is the deepest part of Union Lake?: The deepest charted water on Union Lake lies inside the 110 ft contour, toward the middle of the lake. That contour encloses 4.9 acres, 1% of the mapped water, so it is a small target on a small water, the depth chart above gives the contour to line up on.
How much of Union Lake is shallower than 40 feet?: About half. The 40 ft contour encloses 199 acres of the roughly 467 acres inside the outer 5 ft line, so the other half of the water is shallower than 40 feet. The sharpest drop is between 5 and 10 feet, where the mapped water sheds 131 acres.
How accurate is this Union Lake depth map?: The contours come from the Michigan DNR Inland Lake Contours survey, retrieved August 2026 and last rebuilt on August 19, 2026. Depths change over time with water levels and sediment, so treat this map as a planning guide for fishing, and never use it for navigation. Acreages are computed from the published contour geometry, not from a separate area survey, so read them as close approximations.

Depth maps for lakes near Union Lake

Cooley Lake depth map · 56 ft max · 1 mi away
Green Lake depth map · 72 ft max · 1 mi away
Middle Straits Lake depth map · 55 ft max · 2 mi away
Upper Straits Lake depth map · 96+ ft max · 3 mi away
Cedar Island Lake depth map · 72 ft max · 3 mi away

Mapped fishing venues near Union Lake

Union Lake in the venue directory covers access and fishing details for this water.

Cooley Lake · 1 mi away
Green Lake · 1 mi away
Middle Straits Lake · 2 mi away

Fishing in Michigan needs a state license: Michigan fishing license guide · all Michigan venues