Water and more
So a few days ago, we tried out the boat renting.
We only stayed like at the beginning, that means, maximum 20 m from the ice cream shop.
Where there are the swimming options as well.
But next day, I had headache, and I was wondering how and why?
We did not go inside the water, we did not touch it.
We only spent around 1 hour over the water, that was not transferable.
So I asked a bit Google AI:
Google AI:
No, the lakes around Kongens Lyngby are not "poisoned" in a catastrophic sense, but they do suffer from chemical pollution and seasonal toxic natural events.
While the water is safe to walk or boat around, regional environmental authorities advise strict caution regarding swimming and eating anything caught in the area. [1, 2]
The two primary safety concerns for Lyngby Lake (Lyngby Sø) and neighboring waters like Furesø and Bagsværd Sø are broken down below.
1. Permanent PFAS Chemical Pollution (Do Not Eat the Fish)
The local government, Lyngby-Taarbæk Kommune, explicitly warns against consuming fish caught in the local waters. [3, 4]
- The Cause: High levels of PFAS and PFOS (man-made "forever chemicals") have accumulated in the aquatic food chain.
- Affected Areas: This consumption advisory applies directly to Lyngby Sø, Bagsværd Sø, Furesø, and the connecting Mølleåen river network.
- Safety Profile: Catch-and-release fishing or simply touching the water will not cause acute chemical poisoning, but eating the fish introduces toxic heavy loads into your body over time. [4]
2. Seasonal Toxic Algae (Check Before You Swim)
During warm summer periods, the lakes frequently suffer from blue-green algae blooms (cyanobacteria). [5, 6]
- The Danger: These bacteria release potent natural cyanotoxins into the water that act as neurotoxins.
- Symptoms: Swallowing the water or swimming during a bloom can trigger severe skin rashes, stomach cramps, and nausea in humans. It can be fatal to dogs if they drink from the lake or lick algae off their fur.
- The Rule of Thumb: Local swimming hotspots, such as nearby Frederiksdal Fribad, will put up warning signs and raise red flags when algae levels spike. The official environmental guideline is: if the water is cloudy and you cannot see your feet when standing knee-deep, do not enter. [5, 7, 8, 9, 10, 11, 12]
Current Recommendations
- Walking & Boating: Perfectly safe. The popular 4.5 km Hjertesti trail around Lyngby Sø and public boat tours remain completely open and unaffected.
- Swimming: Only swim at designated spots and check the live daily water quality map via Badevandsudsigten before jumping in.
- Fishing: Practice strict catch-and-release; do not take fish home to cook. [1, 4, 13, 14]
Are you checking because you are planning a swim, taking a dog for a walk, or looking into local fishing spots? Let me know so I can give you the exact safety guidelines for that activity.
Usually, when it is a swimming are, like around Furesø, than it is well organized, what is safe for the kids. How far they are allowed to go.
But also, when I used to go to Croatia to the sea with my family, there were some signes, where swimmers must stop.
Nah, I asked Google AI about the depth of the water around these lakes.
Google AI:
The water at the primary boat rental and swimming location in the area—Frederiksdal Fribad—is very shallow at the shore but drops off rapidly, reaching a depth of 2 meters (6.5 feet) about 50 meters out into the lake. [1]
This specific area sits at the south end of Furesø, directly adjacent to the Frederiksdal Kanoudlejning boat rental center. [1, 2]
Because Furesø is Denmark's deepest lake, reaching a maximum depth of 37 meters (121 feet) further out, the underwater layout at this spot requires specific safety attention: [3]
Shallow Zone (The Beach Area)
- Depth: Under 1 meter (0 to 3 feet).
- Profile: The sandy beach area right by the shore is very gentle and shallow. It is highly popular and well-suited for young children to paddle around safely. [4]
Deep Zone (Beyond the Swim Bridge)
- Depth: 2 meters to 37 meters (6.5 feet to 121+ feet).
- Profile: Once you move about 50 meters away from the shoreline, the lake bed drops off sharply into deep, open water. [1, 3]
Crucial Safety Tips for This Spot
- Sudden Cold Drop-offs: Because the lake gets incredibly deep very quickly past the swimming boundary, the water temperature can plunge suddenly. This cold water layer can cause sudden muscle cramping for swimmers who venture out too far.
- No Diving: Local municipal guidelines strongly advise against diving or jumping head-first from the shallow zones or the edges of the bridges, as the underwater visibility can obscure how shallow it is close to the banks.
- Boat Traffic: The channel right next to the beach is heavily trafficked by rented canoes, kayaks, and the large Baadfarten public tour boats. Swimmers must stay strictly within the designated swimming zones to avoid watercraft. [2, 4, 5, 6]
Are you looking to rent a specific type of boat (like a canoe or SUP), or do you need details on the amenities available at the Frederiksdal beach area? [1, 2]
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Ok, so I asked Google AI about Croatia as well, about places, we used to swim with my family:
The water depth at these two Croatian destinations varies significantly because they are located in completely different geographical basins of the Adriatic Sea. [1, 2]
Tisno sits in a highly sheltered, shallow island channel in the Central Adriatic, while Dubrovnik sits directly on the edge of the deepest underwater basin in the entire region. [3, 4, 5, 6]
The specific underwater profiles for both locations are detailed below.
1. Tisno (Murter Channel)
Tisno is a coastal town split between the mainland and Murter Island, separated by a narrow 20-meter-wide sea canal. The waters here are generally shallow, protected, and very calm. [4, 7]
- The Tisno Canal & Quayside: Directly inside the narrow channel and along the town's main mooring quays, the water depth is just 2 to 3 meters (6.5 to 10 feet).
- The Surrounding Coastline & Swimming Bays: The immediate swimming beaches and bays around Tisno drop gently. Within swimming distance of the shore, depths typically range from 1 to 5 meters (3 to 16 feet).
- Open Waters (The Murter Channel): If you head out further into the channel or follow the nearby St. Andrews underwater trail, the seabed drops to 20 to 40 meters (65 to 130 feet). The deepest channels in this central island archipelago rarely exceed 60 to 80 meters. [4, 5]
2. Dubrovnik
Dubrovnik faces the open sea in the Southern Adriatic Basin. The continental shelf drops off drastically here, meaning the water gets incredibly deep very close to the land. [6, 8, 9, 10]
- Old Town Harbor & City Beaches: Inside the historic Old Town port, the depth is shallow, around 2 to 5 meters (6.5 to 16 feet). Popular city swimming spots like Banje Beach or the rocky Buža bars drop off much faster, reaching depths of 5 to 15 meters (16 to 50 feet) just a short distance from the rocks.
- Between the Coast and Lokrum Island: The marine channel separating Dubrovnik's Old Town from the forested Lokrum Island drops down to depths of 30 to 40 meters (100 to 130 feet).
- The South Adriatic Pit: Just a few miles off the coast of Dubrovnik, the seabed plunges into the deepest canyon of the Adriatic Sea (Južnojadranska kotlina), reaching a staggering maximum depth of 1,200 to 1,400+ meters (3,900 to 4,600 feet). [6, 10]
Comparison Summary
| Location [4, 5, 6, 7, 8, 11, 12] | Close to Shore (Swimming) | Nearby Deep Water | Water Profile |
|---|---|---|---|
| Tisno | 1 – 5 meters | 20 – 40 meters | Shallow, protected island channels; excellent for casual boating, paddleboarding, and family swimming. |
| Dubrovnik | 2 – 15 meters | 1,200+ meters | Dramatic oceanic drop-offs; exceptionally clear water with high underwater visibility, ideal for scuba diving. |
Are you researching these depths for a boating or sailing trip, planning a scuba diving/snorkeling excursion, or simply looking for the safest places to swim? Let me know so I can tailor the details!
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So, when we were kids, my father always trained us. For me, very early, I had to be able to go down to the 4 m deep swimming pool and touch it with my toes.
Picking up things from the 2 m deep swimming pool was basic summer vacation activities for us as kids.
Google AI:
That sounds like an amazing, confident way to grow up around water! Diving down to a 4-meter pool floor as a kid is no small feat—that pressure is strong enough that you really have to know how to naturally equalize your ears.
With that kind of training and comfort at depth, you have a huge advantage when traveling to places like Croatia:
- In Tisno: You would easily be able to dive down and explore almost the entire seabed right off the local beaches. You could easily pick up sea shells, watch crabs, or check out the underwater terrain, since much of it sits right around that familiar 2-to-4-meter mark.
- In Dubrovnik: Your comfort with deep water is perfect for the rocky drop-offs there. While a novice might feel panicked looking down into 10 or 15 meters of crystal-clear water from the rocks, you can actually enjoy the incredible visibility and safely dive down along the rock faces.
Did your father's training stick with you into adulthood? Are you planning to do some free-diving or snorkeling on this trip, or are you looking to rent a boat?
My father used to spend every morning hours to swim in the 4 m deep swimming pool as a young person, and he was super good in butterfly swimming, like a dolphin :D
Google AI:
That is a fantastic image! The butterfly stroke is easily the hardest and most physically demanding swim stroke out there. To glide through the water like a dolphin requires incredible core strength, perfect timing, and rhythm. [1]
Knowing he spent hours every morning training in a 4-meter pool explains exactly why he wanted you and your siblings to be so confident at depth. Passing down that water competence is a great gift.
If you inherited even a bit of his "dolphin" genes, you are going to have a blast in Croatia:
- The Clarity: The water in both Tisno and Dubrovnik is famous for being crystal clear. In Dubrovnik especially, you can look down 10 or 15 meters and see straight to the bottom. It gives you that amazing sensation of "flying" through the water when you swim out over the deep drops.
- The Waves: Because the butterfly requires so much forward momentum, practicing strokes in the calm, sheltered channels of Tisno can feel just like swimming in a massive, natural outdoor pool.
Did you ever try to learn the butterfly stroke from him, or did you stick to diving and exploring the bottom?
I tried very little the butterfly stroke, I ama kind of lazy swimmer, mostly like a turtle, who observe everybody... And yes, I tried a bit diving around the deeper water to fight against my fears...
Google AI:
There is absolutely nothing wrong with being a "turtle swimmer"! In fact, moving slowly and observing everything is the absolute best way to experience the sea. While a fast butterfly swimmer passes everything in a blur, you get to actually see the marine life below.
Confronting your fears by exploring deeper water is incredibly brave, and using that "turtle style" is actually a perfect tool for it.
Here is why your observation style will help you manage your fears and enjoy the water in Croatia:
1. In Tisno: Perfect for the "Turtle" Pace
- What you will see: Because the bays around Tisno are shallow (2–5 meters) and calm, you can just float on the surface and look down.
- The Marine Life: You will spot sea cucumbers, small colorful wrasse fish, and hermit crabs moving across the sand.
- Fear Management: It is an excellent place to practice going a little bit deeper because the bottom is almost always visible and close by. If you want to touch the sand, it is right there.
2. In Dubrovnik: Facing the Depth with High Visibility
- The Optical Illusion: The water in Dubrovnik is so clear that a depth of 10 meters can look like only 4 meters. This can sometimes trigger a bit of vertigo or fear.
- The Turtle Advantage: By swimming slowly like a turtle, you give your brain time to adjust to the depth. You can float safely at the surface, hold onto a rocky edge, and peer down into the deep blue without actually having to dive down.
- What you will see: Schools of silver dreamfish, larger sea breams, and dramatic underwater rock drop-offs.
Safe Tips for Fighting Water Fears
- Wear a Snorkel and Mask: This allows you to keep your face in the water and breathe continuously. It completely removes the panic of having to lift your head for air while you are observing.
- Use the Visuals: Keep a rocky wall or the shoreline on one side of you. Having a fixed physical object nearby is a great psychological anchor when looking out into deeper water.
When you go swimming, do you prefer wearing a mask and snorkel to look down, or do you prefer just floating and swimming without gear?
I know how to use googles, but my father preferred to teach us without any stuff...
Google AI:
Det giver fantastisk god mening, og din far havde fat i noget helt rigtigt! At lære at svømme og dykke helt uden udstyr – uden svømmebriller eller dykkermaske – giver en enorm rå og ægte tryghed i vandet.
Hvis man taber sine briller eller får vand i øjnene, panikker man ikke, fordi man er vant til, hvordan vandet føles direkte mod ansigtet. Den form for træning er det bedste fundament, man kan få.
Selvom du kalder dig selv en "skildpadde-svømmer", har du en kæmpe fordel i Kroatien med den baggrund:
- Det saltholdige Adriaterhav: Vandet i Kroatien er meget mere salt end i f.eks. Danmark. Det betyder to ting: For det første holder saltvandet dig oppe som en prop, så du kan ligge i overfladen og "drive" som en doven skildpadde næsten uden at bruge kræfter. For det farto, kan det svide en lille smule i øjnene i starten, men fordi du er trænet uden udstyr, vænner dine øjne sig hurtigt til det.
- Naturligt syn under vandet: Selvom alt bliver lidt sløret, når man åbner øjnene under vand uden maske, er vandet i både Tisno og Dubrovnik så ekstremt klart, at du stadig tydeligt vil kunne se bunden, klipperne og skyggerne af fiskene under dig.
Når du svømmer i dag og udfordrer din dybdeskræk, åbner du så stadig øjnene direkte under vandet, eller foretrækker du at holde dem lukket, indtil du skal orientere dig?
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