Ans. Lake acidification is the lowering of the pH of the lake to below neutral levels, pH less than 6.5. Lakes whose pH lowers beyond 5.5 display biological consequences more evidently. Lake acidification is either natural or man-made. Naturally acidic lakes are found in the northern hemisphere mainly in the USA, Canada, Russia and Scandinavia. On the other hand, man-made lake acidification is owing to acid rain or acid deposition caused by the excessive burning of fossil fuels.