What is meant by the aging of a lake?

In automobiles,catalytic converters change unburnt hydrocarbons into

Delhi is one of the most polluted cities of the world. Which of the following steps were taken by the government to reduce vehicular pollution in Delhi?
$I.$ Phasing out of old vehicles
$II.$ Use of unleaded petrol
$III.$ Use of low sulphur petrol and diesel
$IV.$ Use of catalytic converters in vehicles
$V.$ Applying stringent pollution level norms for vehicles
$VI.$ Switch over of public transport from diesel/petrol to $CNG$
Which of the statements given above are correct?

The process of aging of a lake by human activities occurs at a very rapid rate,which is called......

The natural aging of a lake by nutrient enrichment of its water is known as $..........$

What does the term 'eutrophic lakes' mean?