during the winter months, one of the things to look forward to is a phenomenon called 'maré roxa', or 'purple tide'.

the purple tide happens after a cold front leaves rio de janeiro, and marine currents coming from the south of brazil get to rio's coastline, paired with winds from the south-west.   

the result is a spectacularly clear, calm, warm crystalline water along the oceanic beaches, with temperatures between 0 and 25 degrees celsius (68 and 77 degrees fahrenheit).