What You'll Find at Grout Bay

Grout Bay is a shallow, tidal embayment in the Sacramento-San Joaquin Delta where the Mokelumne River meets deeper water. It holds striped bass year-round, with spring and fall runs that draw anglers targeting 15- to 25-pound fish. White sturgeon to 5 feet are present but less predictable. The bay itself is narrow and protected, making it manageable for small boats and kayaks, though current and tidal swing demand respect.

Access is limited to boat launch only — there is no bank fishing. The nearest public launch is at Thornton, about 3 miles upriver. Tides control fishing windows here more than most Delta locations; slack water and the first two hours of incoming tide are the most productive periods. Striped bass feed on shad and threadfin herring, so live bait and shad-pattern swimbaits work consistently.

Key Takeaways

  • Grout Bay holds striped bass year-round, with peak fishing in April through May and September through October when larger fish move through the Delta.
  • You must launch a boat at Thornton or another Delta ramp; there is no shore access to Grout Bay itself.
  • Tidal current is strong enough to affect boat positioning and bait presentation, so plan your trip around slack water or the first hours of incoming tide.
  • Live threadfin herring and shad are the most reliable baits; striped bass also respond to 3- to 4-inch swimbaits worked along channel edges.
  • A California fishing license and Delta waterway permit are required; sturgeon retention is catch-and-release only in most years.

Seasons and What to Expect

Spring (March through May) is the strongest season. Striped bass migrate upriver to spawn, and Grout Bay sits on a major corridor. Fish in the 18- to 28-pound range are common, and you may encounter larger specimens. Water temperature climbs from the low 50s to the mid-60s, and visibility improves. Mornings are typically calmer than afternoons, and the incoming tide from 8 a.m. to noon often produces steady bites.

Summer (June through August) slows considerably. Water warms to the high 70s and low 80s, and striped bass move deeper or toward cooler water near the Delta's western channels. Fishing is possible but requires patience and early starts. Fall (September through October) rebounds sharply as water cools and another wave of striped bass enters the Delta. October often rivals April for consistent action.

Winter (November through February) is slow and unpredictable. Striped bass are present but scattered, and cold water, short days, and occasional rain make the bay less attractive than other Delta locations. Some anglers fish it during winter for the solitude and the chance at a large fish, but success rates drop noticeably.

How to Reach Grout Bay and Launch Your Boat

Grout Bay lies in San Joaquin County, roughly 15 miles south of Lodi. The primary public launch is at Thornton, operated by San Joaquin County Parks. From Highway 99, take the Thornton Road exit and follow signs to the launch area. The ramp is concrete, well-maintained, and has parking for trailers. There is a day-use fee, typically $5 to $10, though rates vary seasonally.

From Thornton, head downriver (south) on the Mokelumne River. Grout Bay opens to your left (east) after about 3 miles. The bay is marked on navigation charts and is easy to identify — it widens noticeably and the current slackens. If you are unfamiliar with Delta navigation, consider hiring a guide for your first trip; the channels are well-marked but tidal current and shallow spots require attention.

Alternative launches include Locke Regional Access (north of Thornton) and various private marinas in the area. Locke is smaller and less crowded but has fewer amenities. Call ahead to confirm hours and fees, as they change seasonally and can be affected by water conditions.

Tides, Current, and Timing Your Trip

Tidal swing in Grout Bay can exceed 3 feet, and current speeds reach 1 to 2 knots during peak flood and ebb. This is not dangerous for experienced boaters but requires planning. Slack water — the 20 to 40 minutes when current pauses between flood and ebb — is the easiest time to fish. Striped bass feed most actively during slack and the first two hours of incoming (flood) tide.

Check tide tables for the Mokelumne River or Stockton before you launch. NOAA provides free tide predictions online; enter "Mokelumne River" or "Stockton" as your reference station. Plan to launch 30 to 60 minutes before slack water so you are positioned and ready when feeding begins. If you arrive during strong ebb (outgoing) tide, you may spend your first hour simply holding position rather than fishing.

Water clarity varies with season and recent rainfall. Spring runoff can cloud the bay for weeks. Fall and winter typically offer the clearest water. Striped bass rely on sight and vibration to find bait, so live bait often outperforms lures in murky conditions.

Baits, Lures, and Rigging

Live threadfin herring (shiners) are the gold standard at Grout Bay. They are available at most Delta bait shops and are hardy enough to survive the boat ride and tidal current. Fish them on a simple sliding sinker rig: 1/2-ounce egg sinker, barrel swivel, 18-inch leader of 20-pound monofilament, and a size 2/0 to 3/0 circle hook. Cast uptide and let the current carry the bait; striped bass will take it on the drop or as it swings.

Live shad (Sacramento splittail or threadfin) work equally well and are sometimes easier to find in fall. Swimbaits — 3 to 4 inches, shad-colored — are effective when live bait is scarce. Fish them on a 1/4-ounce jighead or a drop-shot rig along channel edges and deeper holes. Jigging spoons (1/2 to 1 ounce) can produce in deeper water but are less consistent than live bait in Grout Bay's shallow, current-swept environment.

Sturgeon, if you encounter one, rarely takes a striped bass rig. They feed on the bottom and prefer fresh shrimp, ghost shrimp, or cut mackerel on a heavy sinker. Sturgeon fishing in California is heavily regulated; check current regulations before targeting them, as retention is closed in many years.

Regulations and Licensing

A valid California fishing license is required for anyone 16 and older. Licenses are sold online through the California Department of Fish and Wildlife website, at sporting goods stores, and at many bait shops. A one-day license costs less than a full-year license and is a good option if you fish only occasionally.

The Delta Waterways Permit is a separate requirement for fishing in the Sacramento-San Joaquin Delta. It is free and can be obtained online or at launch facilities. Some launches issue it on-site; others require you to print it beforehand. Carry both your fishing license and the permit in your boat.

Striped bass have a 2-fish daily limit and a 12-inch minimum size in most years, though regulations can change. White sturgeon is catch-and-release only in recent seasons; check the current regulations before you fish. Regulations are posted on the California Department of Fish and Wildlife website and at launch areas. When in doubt, ask the launch attendant or call the regional office.

Boat Type and Safety Considerations

A 16- to 20-foot center console or open boat is ideal for Grout Bay. The water is shallow (4 to 12 feet in most areas) and the bay is narrow, so a shallow-draft hull and a tiller or small outboard are sufficient. Kayaks and small jon boats work but offer less protection from wind and current. If you are new to boating, rent a boat with a guide rather than launching your own.

Wear a Coast Guard-approved life jacket at all times. Current in the Mokelumne River can be deceptive; a small boat can be swept into a channel faster than you expect. Carry a radio or cell phone, though reception in the Delta can be spotty. Let someone on shore know your launch time and expected return. Avoid fishing alone if possible.

The bay can get choppy in afternoon wind, especially in summer. Launch early and plan to be off the water by early afternoon. Fog is common in fall and winter; carry a compass or GPS and know how to navigate by landmarks if visibility drops.

Frequently Asked Questions

Can I fish Grout Bay from shore?

No. Grout Bay is surrounded by private land and tidal marsh. Boat access only. The nearest shore fishing is at Thornton or along the Mokelumne River upstream, though those areas are less productive for striped bass than the bay itself.

What is the best time of day to fish?

Early morning (sunrise to 10 a.m.) is most productive, especially if it coincides with slack water or the start of incoming tide. Afternoon wind and boat traffic make fishing harder. Plan your launch to arrive at slack water, not after.

Do I need a guide to fish Grout Bay?

Not if you are an experienced boater and familiar with tidal navigation. If you are new to the Delta, a guide will save you time and frustration. Guides know the current conditions, the best bait sources, and how to position your boat in tidal current. Half-day trips run $300 to $500.

What size striped bass should I expect?

Spring and fall runs bring fish in the 15- to 28-pound range. Summer and winter fish are smaller and less predictable. A 20-pound striped bass is a solid catch; anything over 25 pounds is a good day. Sturgeon, if present, are typically 3 to 5 feet and are rarely kept.

Is the water safe to drink or swim in?

No. The Delta is agricultural and urban runoff, and water quality varies. Do not drink untreated water. Swimming is not recommended due to current, boat traffic, and water quality. Wash your hands after handling fish and before eating.