The first time I dropped the hook in the Rade d'Agay, a French sailor rowed across in his tender and, in careful English, asked me to lift it and move thirty metres west. I bristled, then I looked over the side. My chain was lying across a dark green carpet of Posidonia, and twenty metres away there was a clean patch of sand I had simply not bothered to find. He was right and I was lazy. That afternoon changed how I anchor on this coast, and it is the reason I write this.
Why the seabed under your keel matters
Posidonia oceanica is a flowering plant, not an alga, and it grows only in the Mediterranean. It forms meadows from roughly one metre down to forty metres in clear water, and those meadows do an extraordinary amount of work: they shelter fish nurseries, oxygenate the water, lock carbon away, and hold the sand in place so the beaches behind you do not wash away. People call it the lungs of the Mediterranean, and the label is earned.
The catch is how slowly it grows. Posidonia spreads at a few centimetres a year. An anchor that drags through a meadow tears out plants that took a century to establish, and the scar it leaves can take decades to heal, if it ever does. One careless boat does measurable harm. Multiply that by every yacht in every photogenic bay between Saint-Raphael and Menton across a single August, and you see why France finally lost patience.
The rules are no longer advisory
This stopped being a question of manners in 2019. France now bans anchoring over Posidonia for vessels over 24 metres, with the framework built up through decrees since 2016 and tightened in 2020 and 2021 along the Provence coast, the Cote d'Azur and around Corsica. The penalties are not symbolic. A skipper caught damaging a protected meadow can face fines reaching 150,000 euros, with the worst cases carrying the threat of imprisonment and a ban from navigating in French Mediterranean waters.
The 24 metre line is where the hard law currently sits, but the principle applies to all of us. Individual bays now ban anchoring outright for every size of boat, or require you to pick up a laid mooring instead, and the protected zones grow most years. If you want the full picture of where the boundaries fall and how they keep moving, I keep a running account in my notes on the Posidonia anchoring ban in France, and a broader read of the regional restrictions sits in my guide to anchoring rules on the Cote d'Azur for 2026.
Reading the bottom by eye
In Riviera water this is genuinely easy once you train your eye, and it is the single skill that matters most. Put on polarised sunglasses, stand at the bow with the sun behind you, and the contrast is obvious:
- Bright, pale, sandy patches are clean holding ground. Aim here.
- Dark green to brown areas with a lawn-like texture are seagrass. Stay off them.
- A mottled bottom is broken meadow threaded with sand lanes. Pick the clear lanes.
The discipline is to send a competent crew member to the bow to con you onto sand while you work the helm and windlass. Drop precisely, not approximately. If you cannot see a sand patch big enough to swing over, the bay is telling you something.
The apps that map the meadows
You no longer have to guess. The Donia app, developed by Andromede Oceanologie and running since 2013, charts the Mediterranean seabed in detail and shows exactly where the Posidonia lies and where the sand is. Your boat appears over a simplified seabed map and you choose a clean spot before you even slow down. For the French Med it is close to essential kit.
Navily, which most of us already use to read other cruisers' anchorage notes, also flags Posidonia at anchorages and lets sailors report the bottom type, so the seabed shows up on the anchorage page. Between the two you can plan a stop the night before and arrive knowing whether there is sand to drop on or whether you should be hunting for a buoy.
Buoy fields and the honest alternative
In the busiest and most fragile spots, the right answer is increasingly not to anchor at all. Marine parks and protected bays along this coast have laid fields of eco-moorings fixed to the seabed so boats can stop without dragging a chain through the meadow. Some are free, some carry a modest fee, and in popular bays they are gone by mid-morning in season, so come early.
Where there is no buoy and no sand, the disciplined choice is to move on. That is hard on a hot afternoon when the crew want to swim, but it is the correct one. A bay full of yachts swinging on chains over living seagrass is not a holiday postcard, it is a slow-motion mistake repeated a thousand times.
A workable routine looks like this:
- Check Donia or Navily for the seabed before you commit to a bay.
- Look for a laid mooring first and take it if one is free.
- If anchoring, con onto clean sand from the bow. Never drop blind onto a dark bottom.
- Use enough scope to hold safely, but remember a wider swing sweeps a wider arc, so balance security against the ground you disturb.
- Retrieve by motoring up over the anchor, not by dragging it sideways out of the bottom.
Scope, swing and the moment of setting
The way you set and the scope you let out both decide how much seabed you touch. A boat at anchor does not sit still, it swings in a circle whose radius is your scope plus the boat length, and everything inside that circle gets swept by the chain as the wind and current shift. On sand that is harmless. Over a patchwork of sand and meadow it means your chain will eventually find the grass even if your anchor landed on clean ground.
So think about the whole swing, not just the drop. Pick a sandy patch big enough that your likely arc stays clear of the dark areas, and favour an all-chain rode with a snubber over a long nylon scope when the holding is good, because chain that lifts cleanly off the bottom as the load comes on disturbs less than a warp dragging back and forth. In settled summer weather on the Riviera you rarely need the heroic scope you would lay in an Atlantic gale, and a tighter, well-set anchor on sand beats a sprawling one whose chain rakes the meadow all night.
When you set, back down gently and watch the anchor, not just the snubber. A snatching, jumping anchor that will not bite is dragging, and a dragging anchor over Posidonia is the worst of both worlds: it does not hold you and it ploughs the meadow. If it will not set first time on what looked like sand, lift cleanly and try again rather than gunning the engine astern and hoping.
Crowded bays and two anchors
The other trap is summer crush. When a bay is packed, the temptation is to wedge in anywhere and let out short scope, which both reduces your holding and increases the odds your chain ends up on grass you did not mean to touch. In tight, sandy anchorages a Mediterranean mooring with two anchors can let you sit on a smaller, cleaner footprint, and I walk through the technique in my piece on using two anchors in a crowded bay. It is a useful tool, but it is no substitute for finding sand in the first place.
The payoff is the thing you came for
Anchoring well over seagrass costs nothing but a few minutes of attention. You read the bottom, you drop on sand, you take a buoy where one is laid, and you sail on where the holding is wrong for the meadow. In return you keep the water clear enough to see your anchor on the bottom, the fish abundant enough to watch from the swim ladder, and the snorkelling worth the dinghy ride ashore.
That French sailor in his tender was not lecturing me. He was protecting the thing that made the bay worth visiting. These days I am the one keeping half an eye on where other boats drop, and when I see a chain settling onto a dark patch I think of him, and I find I have become exactly the kind of guest this coast needs more of.
