What Four Tree Island Offers

Four Tree Island sits in the middle of Portsmouth Harbor, roughly equidistant from the New Hampshire and Maine shores, and it's one of the most reliable shallow-water spots for striped bass and summer flounder in the entire harbor system. The island itself is small and rocky, but the real fishing happens in the water around it—a mix of sand and mud bottom in 8 to 15 feet of water that holds fish year-round. The shelter the island provides from wind and chop makes it fishable on days when the open harbor gets too rough, and the tidal current that funnels through the surrounding channels concentrates baitfish and the predators that hunt them.

Access is by boat only, and you'll need to launch from one of Portsmouth's public ramps or a private marina. The island itself is not a landing spot—it's protected habitat—but the water around it is open to fishing. Most anglers work the deeper channels on either side of the island, casting toward the shallower edges where structure meets open water.

Key Takeaways

  • Four Tree Island holds striped bass and flounder in 8 to 15 feet of water, with the best fishing on the sand and mud flats surrounding the rocky core.
  • Spring and fall bring the most consistent striped bass activity, while summer flounder peak from June through September.
  • Slack water and the first two hours of incoming tide are usually more productive than hard outgoing current, which can sweep bait and lures away too quickly.
  • You must launch by boat from Portsmouth; the island itself is off-limits to landing, but the surrounding water is open to fishing.
  • Eels, live mackerel, and soft plastics in natural colors work best; the water clarity here is moderate, so bright lures are less effective than subtle presentations.

Seasonal Patterns and What to Target

Spring stripers (April through May) move through Portsmouth Harbor on their way north, and Four Tree Island sits directly in their migration corridor. Fish 8 to 12 feet of water with live eels or large soft plastics—the bass are feeding aggressively after winter and will chase moving baits. Early morning and late afternoon are most productive, but the bite can hold all day if the water temperature is still cool.

Summer (June through August) shifts the focus to flounder. The bottom around Four Tree Island warms up, and flounder move in to hunt. Fish the flats in 10 to 14 feet of water with live mackerel or squid on the bottom, or work soft plastics slowly along the edges. Stripers are still present but less predictable; they tend to move deeper or into shadier channels during the heat of the day.

Fall (September through October) brings another strong striped bass bite as fish move south and feed heavily before winter. The water cools, baitfish concentrate, and the current patterns stabilize. This is often the most consistent season at Four Tree Island—fish the deeper channels on both sides of the island with eels or live mackerel.

Winter fishing is possible but requires patience. Water temperatures drop into the 30s, and fish move to the deepest holes in the harbor. Four Tree Island becomes less productive than deeper channels nearby, but if you're targeting winter stripers, the 15-foot holes just beyond the island can hold fish on slack water.

Tides, Current, and Timing

Four Tree Island sits in a funnel where current accelerates, which means tide timing matters more here than in many other harbor spots. Slack water—the 20 to 40 minutes around high and low tide when current nearly stops—is usually the most productive window. During slack, baitfish settle, and predators hunt more actively. Hard outgoing current can be productive if you're drifting live bait, but incoming current often pushes bait and lures away from the island too quickly.

The first two hours of incoming tide are often better than the last two hours of outgoing. If you're fishing with artificials, work the shallower edges (8 to 10 feet) on incoming tide and the deeper channels (12 to 15 feet) on outgoing. The island itself creates a slight eddy on the back side during strong current, which can concentrate fish.

Check tide tables for Portsmouth Harbor before you launch. The timing shifts by roughly 50 minutes each day, so a good morning bite one day might be an afternoon bite the next. Many anglers fish the slack water windows and leave when current picks up, rather than fighting hard current all day.

Tackle and Bait That Work

Live eels are the most reliable bait for striped bass at Four Tree Island. Fish them on a simple 1/0 to 2/0 circle hook with a small split shot 18 inches above the hook to keep them near bottom. Cast uptide and let the current carry the eel toward the island, then work it slowly back. Eels stay alive longer in the moderate current here than in faster-moving rivers, so you can fish the same eel for 30 minutes or more.

Live mackerel work well for both stripers and flounder, especially in summer. Use a 2/0 to 3/0 hook and fish on the bottom or suspended 2 to 3 feet above it, depending on where you see baitfish on your sounder. Squid is a good backup when mackerel is hard to find, though it doesn't stay on the hook as long in current.

Soft plastics in natural colors—pearl, white, and natural shad patterns—outfish bright colors here. The water around Four Tree Island has moderate clarity, and subtle presentations work better than flashy lures. Fish 3 to 4-inch shad-pattern plastics on a 1/4-ounce jig head, working them slowly along the bottom or in the water column. Larger plastics (5 to 6 inches) can draw stripers, especially in fall.

Small metal jigs (1/2 to 1 ounce) can work on the deeper edges, particularly when current is strong. Cast uptide and let the jig fall on a tight line, then retrieve with a slow, steady pace. This approach is less productive than live bait but can be effective when you're covering water quickly.

Launching and Navigation

The closest public boat launch is at Marcy Street Park in Portsmouth, roughly 1.5 miles south of Four Tree Island. The ramp is concrete, well-maintained, and has parking for trailers. From there, head north into the harbor and follow the main channel markers. Four Tree Island is clearly visible and sits roughly in the middle of the harbor between the New Hampshire and Maine shores.

If you're launching from a private marina, ask the harbormaster for directions to Four Tree Island and confirm that your boat is appropriate for the harbor. Most small center-console boats and open skiffs work well here; the water is generally calm inside the harbor, but the entrance can get rough on windy days.

Navigation is straightforward—the island is a visual landmark and sits in open water with no hidden rocks or shoals immediately around it. Use your sounder to find the 8 to 15-foot zone and the sand-mud bottom. Anchor uptide of where you want to fish and let the current carry your bait or lures toward the island.

What to Expect and Common Mistakes

Four Tree Island is not a secret spot, and you'll often share the water with other anglers, especially on weekends and during peak season. The fishing is consistent enough that it's worth the company, and the harbor is large enough that you can usually find a quiet edge if you arrive early or fish during the week.

The most common mistake is fishing too hard on outgoing current. Many anglers assume that faster current means more feeding, but at Four Tree Island the opposite is often true. Slack water and the first part of incoming tide produce more bites. If you're getting no strikes during hard current, move to a different tide window rather than grinding it out.

Another mistake is using lures that are too bright or too large. The water here is not gin-clear, but it's not murky either. Subtle presentations work better than flashy ones. If you're not getting strikes with bright lures, downsize and switch to natural colors.

Finally, don't anchor directly on the island. Fish the channels and flats around it, keeping at least 50 to 100 feet of distance. This keeps you in productive water and respects the protected habitat of the island itself.

Frequently Asked Questions

Can I fish Four Tree Island year-round?

Yes, but winter fishing is slow. Spring through fall offer the most consistent action. Winter stripers are possible in the deeper holes nearby, but Four Tree Island itself becomes less productive as water temperatures drop and fish move to deeper channels.

What's the best time of day to fish here?

Early morning and late afternoon are usually most productive, but slack water windows (around high and low tide) often produce better than time of day. A good slack water bite at midday will outfish a poor current window at dawn.

Do I need a boat to fish Four Tree Island?

Yes. The island is in the middle of Portsmouth Harbor and is accessible only by boat. Launch from Marcy Street Park or a private marina in Portsmouth.

What size fish should I expect?

Striped bass here range from 18 inches to over 40 pounds, with most fish in the 20 to 30-inch range. Summer flounder typically run 16 to 24 inches. The harbor holds some larger fish, but consistent catches are in the keeper range.

Is the island itself open to landing?

No. Four Tree Island is protected habitat and off-limits to landing. Fish the water around it only.