Finding estuary structure
  |  First Published: December 2009

For a large majority of anglers in our tidal estuaries, finding a likely spot to soak a bait or toss a few lures is largely based on escaping any prevailing winds or strong currents for the angler’s comfort, rather than the fishing prospects below the surface.

This usually means most boats anchored on the inside or outside of major bends or inside sheltered bays and inlets.

While the odd fish may be caught by this ‘lucky dip’ method, finding a little bit of structure that has concentrations of bait and/or feeding fish is a far better proposition. Securing a feed will be more successful and will make braving the elements a little easier to fathom.

In this article we’ll look at finding structures on the riverbed.

If you have just had the thought that you don’t own a sounder, you fish from a kayak or are land-based, don’t worry too much. And even if you have a depth sounder, you will still benefit from reading on.

Before the wide availability and affordability of modern sounders, anglers had to find structure to fish by other means.

It’s an art that is all but lost to most modern-day anglers, who use sounder/GPS combos and common knowledge of local spots.

Using the information in this article will help you to find the best structure at well-known spots and to find new structure, not often fished, even while travelling at a rate of knots between spots.

All of this relates to reading the surface of the water and the geographical composition of the surrounding landscape to unravel the secrets below.

Any decent piece of structure below the surface in our tidal estuaries displaces the water that flows in its vicinity. On the surface, the displaced flow can be seen as boils, current lines, pressure waves and upwellings.

They may also incorporate colour changes as well, from the turbulence created by the displacement of water.

These indicators can be easily seen on the surface either up- or down-current of the structure, depending on the make up of what is creating the disturbance and the strength of the tide on a given day.


A great example of reading the surface can be had around bridge pylons in tidal systems.

Next time you’re passing by, take a moment to observe the effects the pylons have on the water moving by them.

Generally, on the up-current side of the pylons there will be a pressure wave. Depending on current strength, it could be a 10cm in front or almost a metre on the larger spring tides.

The pressure created from the prevailing tide creates a pocket of slack water that eddies within itself, which in turn enables bait and predators to hold ground comfortably with minimal effort.

Baitfish will often hold in the upper half of the water column here, feeding on micro organisms, small bait like ‘eyes’ and glass prawns, while predatory fish will sit in the bottom half of the water column and feed on the bait above.

They’ll also break cover to grab any poor morsels that are being swept by in the tide, and then return to the pocket of slack water to digest their meal and prepare for the next assault.

When fishing this type of structure, the angler should focus the majority of his/her time fishing here for best results.

Behind the pylons will be a rather large amount of broken, swirling eddies created by the displacement of water from the pylons.

From my experience, I don’t regard this water to be as productive as the pressure wave in front of the pylon. Fish can still be found and caught here but I have found the majority of active catchable predators such as mulloway, flathead, kingfish, bass and mangrove jacks hold up in front of the pylon, in prime position.

The aforementioned example can be used when looking for subsurface structure in the form of reefs, wrecks and drop offs.


Instead of being able to see the structure creating the surface formations, you will be looking specifically for the signs of displacement on the surface.

The task of seeing these formations will be made difficult in windy and choppy conditions so make the most of those calm, glassy days by exploring and marking likely signs.

Some trial and error will be needed to work out the best tide and method to fish each individual structure.

Some may fish well on an outgoing tide, some on the incoming tide and some right on slack water.

On my ‘local’, the Hawkesbury River, there are two reefs that produce fish only on slack water. It took a few trips and a lot of lost lures during the run of the tide on the snaggy terrain beneath, for the penny to drop.

When we decided to have a flick around on the slack water between the tides results were immediate, with a 94cm jewfish hitting the deck after two casts.

I found I could cover the area quickly and efficiently with lighter, more natural-looking lures and maintain great contact with my jig, feeling every bit of reef, weed and, most importantly, bites.

Another example of trying a variety of different tide cycles on a chosen location is a little-known spot I found by using observations previously mentioned.

It consists of a shale ledge in the middle of a flat, barren section of river. One would first think that fish would hold on the down-current, deeper side of the drop-off. Not so.

In this particular case, the fish would feed aggressively on the tides that push straight into the rising structure, which created a pocket of water that held the bait and in turn the predators such as jewfish, flathead and bream.

Once a likely spot has been identified through your observations of the surface or the surrounding landscape, a quick run over the area with a good sounder will affirm or dispel the assumption of bottom structure.


If the area has what you’re looking for in the way of structure, the next process is to map it.

Before I had a depth sounder I would use a soft plastics rigged on a jig head. I’d cast all around the area, making contact with the bottom regularly and noting any feeling of reef. If there was an extended time before it hit the bottom after I jigged the lure, this indicated to me a sudden drop-off and likely fish-holding structure which would warrant just one more cast!

Nowadays though, a depth sounder is much quicker and easier for locating the best bits of the structure.

Used in conjunction with the details of the surface formations, the more displacement (boils, upwellings, colour changes), the better the structure. Anglers should focus around here.

When mapping a spot. I visualise what the sounder is showing me to gain an overall picture of the area and the most likely places to focus my effort.

In an estuary there will be prominent features in the landscape above the water. If you don’t own a GPS, these should be used to take a position or a mark for a reference to return to.

Try to draw a straight line between two objects, such a tree on one bank and a channel marker on the other. If the structure is in open water, a third indicator can aid you to stay better positioned without as much guesswork to hold a particular distance off the shoreline.


An alternative method of choosing a likely spot, which can be beneficial when the wind is chopping up the surface and making it hard to read, is the geographical makeup of the land that surrounds you.

Landslides, fallen rocks and the natural lie of the land, such as escarpments, valleys, ridges, swamps and salt marshes, can all hold clues to good fishing spots nearby. These apply on your local waterway and faraway destinations that you’re trying to nut out.

Closely analysing and investigating any abnormalities in the surroundings, such as a few 40cm rocks visible only at low tide on a long featureless mud or sand flat, could lead the angler to stumble across a rock bar that extends strongly below the surface.

Such a place is likely a prime spot to target flathead, jewfish, bream and, further north, mangrove jacks.

Everything is worth investigating, especially if it’s a slow day on the catching front.

While motoring around, studying the sides of the ridges and escarpments that fringe a river or lake has led me to some new ground on more than one occasion.

I detected an indent in the side of a cliff face that had vegetation slightly out of place with the rest of the face. I speculated it could well have been made from a substantial landslide, even hundreds of year ago.

A quick run with the depth sounder over the water below the indent revealed the landslide and a sizeable reef. This area has become one of my more consistent jewfish reefs in the upper Hawkesbury.


Another scenario in tidal estuaries to prospect with bait or lure is where long stretches of mangroves, reeds or weeds meet a steep natural rock wall. These are easily spotted from a moving boat.

Generally speaking, the side with the mangroves, reeds or weed will be fairly flat and shallow but the bottom will usually drop into deeper water where it meets the rock wall.

This is a prime place for any flathead, jew, bream, bass or estuary perch to feed, especially on a falling tide when the prawns, shrimps and baitfish have to move off the flats and seek refuge in deeper water.

Observing the environment that surrounds us while we’re on the water is a vital element of fishing.

Don’t be scared to experiment and investigate anything that looks different. The day you do could change the way you fish – it certainly did for me!



Make yourself a sounding rope. You can drift through an area with a heavy, streamlined weight (so as to not snag up frequently) on a rope marked in feet or metres, lowering and raising it when necessary to mark the structure down below. This an old, yet very effective way to gauge depth and bottom contours.

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