It's a Panzer IVD of the 31st Panzer Regiment assigned to the 5th Panzer Div. commanded by Lt. Heinz Zobel lost on May 13th, 1940. The "lake" is the Meuse River. The man is a German pioneer.

All credit to finding the Panzer of the Lake goes to ConeOfArc for coordinating the search, and miller786 and their team for finding the Panzer. Full sources and details are in Panzer Of The Lake - Meuse River Theory

The Panzer and the "Lake"

The photo was taken about coordinates 50.29092467073664, 4.893099128823844 near modern Wallonia, Belgium on the Meuse River. The tank was not recovered until much later in 1941. The man is an unnamed German pioneer likely at the time of recovery.

Comparison of an alternative original photo and the most recent image available of the location (July 2020, Google Street View)

On May 12th, 1940 the 31st Panzer Regiment, assigned to the 5th Panzer Division, attempted to capture a bridge over the Meuse River at Yvoir. The bridge was demolished by 1st Lieutenant De Wispelaere of the Belgian Engineers.

Werner Advance Detachment (under Oberst Paul Hermann Werner, commander, 31st Panzer Regiment), which belonged to the 5th Panzer Division, under Rommel’s command... Werner received a message from close support air reconnaissance in the afternoon that the bridge at Yvoir (seven kilometers north of Dinant) was still intact. He (Werner) immediately ordered Leutnant [Heinz] Zobel’s armored assault team of two armored scout cars and one Panzer platoon to head to the bridge at top speed... Belgian engineers under the command of 1st Lieutenant de Wispelaere had prepared the bridge for demolition while a platoon of Ardennes Light Infantry and elements of a French infantry battalion screened the bridge... Although the last soldiers had already passed the bridge, de Wispelaere delayed the demolition because civilian refugees were still approaching... two German armored scout cars charged toward the bridge while the following three Panzers opened fire. De Wispelaere immediately pushed the electrical ignition, but there was no explosion... Wispelaere now left his shelter and worked the manual ignition device. Trying to get back to his bunker, he was hit by a burst from a German machine gun and fell to the ground, mortally wounded. At the same time, the explosive charge went off. After the gigantic smoke cloud had drifted away, only the remnants of the pillars could be seen.

A few kilometers south at Houx, the Germans used a portion of a pontoon bridge (Bruckengerat B) rated to carry 16 tons to ferry their 25 ton tanks across.

By noon on May 13, Pioniere completed an eight-ton ferry and crossed twenty anti-tank guns to the west bank, however to maintain the tempo of his divisions advance, he needed armor and motorized units across the river. Rommel personally ordered the ferry converted to a heavier sixteen-ton variant to facilitate the crossing of the light Panzers and armored cars. Simultaneously, the Pioniere began construction on a bridge capable of crossing the division’s heavier Panzers and motorized units.

Major Erich Schnee in “The German Pionier: Case Study of the Combat Engineer’s Employment During Sustained Ground Combat”

On the evening of the 13th, Lt. Zobel's tank is crossing. Approaching the shore, the ferry lifts, the load shifts, and the tank falls into the river.

The panzer IV of Lieutenant Zabel [sic] of the 31. Panzer Regiment of the 5. Panzer-Division, on May 13, 1940, in Houx, as good as underwater except for the vehicle commander’s cupola. Close to the west bank, at the pontoon crossing site and later site of 5. Panzer Division bridge, a 16 tonne ferry (Bruckengerat B) gave way to the approaching shoreline, likely due to the rotating movement of the panzer, which turned right when disembarking (the only possible direction to quickly leave the Meuse’s shore due to the wall created by the rail line). The tank would be fished out in 1941 during the reconstruction of the bridge.

The Man

Sometime later the photograph was taken of a German pioneer infantryman looking at the tank. Later the tank was recovered and its ultimate fate is unknown.

Available evidence suggests the soldier in the photo is a Pioneer/Tank recovery crew, holding a Kar98k and wearing an EM/NCO'S Drill & Work uniform, more commonly known as “Drillich”.

His role is proven by the presence of pontoon ferries on the Meuse river, used by the 5th Panzer Division. That is also proven by his uniform, which, as evidence suggests, was used during work to prevent damage to their standard woolen uniform.

German pioneers prepare Panzer IIs for ferry crossing

An early version of the Drillich

My own speculation and research prior to the discovery.

While I can't identify the photo, I can narrow down the tank. I believe it is a Panzer IV D.

It has the short barrelled 7.5 cm KwK 37 narrowing it down to a Panzer IV Ausf. A through F1 or a Panzer III N.

Both had very similar turrets, but the Panzer III N has a wider gun mantlet, a more angular shroud, and lacked (or covered) the distinctive angular view ports (I believe they're view ports) on either side of the turret face.

Panzer III N in Italy 1944. source

This leaves the Panzer IV. The distinctive cupola was added in model B. The external gun mantlet was added in model D.

Panzer IV model C lacking the external gun mantlet. source.

Panzer IV model D in France 1940 with the external gun mantlet and periscope. source

Note the front half of the turret top is smooth. There is a protrusion to the front left of the cupola (I believe it's a periscope sight) and another circular opening to the front right. Finally, note the large ventilation hatch just in front of the cupola.

Model E would eliminate the ventilation hatch and replace it with a fan. The periscope was replaced with a hatch for signal flags.

Panzer IV model E lacking the periscope and ventilation hatch. source.

Panzer IV model D entered mass production in October 1939 which means it would be too late for Poland, but could have seen service in France, Norway, or the Soviet Union.

As for the soldier...

The rifle has a turned down bolt handle, a bayonet lug (missing from late rifles), a distinctive disassembly disc on the side of the stock (also missing from late rifles), no front site hood (indicative of an early rifle), and you can just about make out extra detail in the nose cap (also early). This is likely an early Karabiner 98k which is missing its cleaning rod. See Forgotten Weapons: Evolution of the Karabiner 98k, From Prewar to Kriegsmodell.

UPDATE

ConeOfArc posted a video The Search for Panzer of the Lake.

He broke down what he could identify about the solder, probably German.

• German winter style lower.
• German wool tunic.
• M34 Army Standard cap.
• Kar98 rifle missing the cleaning rod.

For the tank he confirms it's a Panzer IV D using similar criteria I used and he found two additional photos of what appear to be the same tank claiming to be from the Western front in 1940.

He then found a Russian source claiming it was found in Romania at the onset of Barbarossa in 1941.

Unfortunately that's all for now. ConeOfArc has put a bounty of $100 US for definitive proof of the tank's location. More detail can be had on ConeOfArc's Discord.