Łacha, Oxbow lake in Nowa Wieś, Józefów, Poland

Łacha, also called Jezioro Łacha or Łacha Nowowiejska, is an oxbow lake of the Vistula in the Nowa Wieś neighbourhood of Józefów, Mazowieckie Voivodeship, just south of Warsaw's border. The elongated water body lies on the Vistula's right-bank floodplain: its right shore is a 3–4 m high escarpment of the Praski terrace, while the left bank is about 1.7 m high.

Łacha is a former channel of the Vistula cut off from the main river; a connection with the Vistula still existed in the early 1980s. A second connection at the southern end was destroyed by earthworks. Since the early 1990s, intensive earthworks at that end have damaged the shoreline and vegetation.

The lake is fished by the Polish Angling Association (PZW), and anglers call the invasive brown bullhead \"byczek\". In 2015 the local PZW club, with ichthyologists from the University of Warmia and Mazury, used a generator to estimate its numbers, catching about 30 kg in one day and estimating several tonnes in the lake. Trap nets called racznik removed over 5,000 bullheads by August that year.

The oxbow lies in Józefów's Nowa Wieś district, just south of Warsaw's border, on the right bank of the Vistula. Its right shore is a 3–4 m high terrace scarp, while the left bank is about 1.7 m high. Water levels vary with seepage from the Vistula, and cold springs rise from the lake bed.

The lake's water level rises and falls with seepage from the Vistula through the ground, and cold-water springs feed the bottom. In 2015, electrofishing caught about 30 kg of invasive brown bullhead in a single day, leading scientists to estimate several tonnes in the lake; over 5,000 were removed with trap nets by August.