If a big lake is covered all around by long kusa grass, just like columns, the waters dry up. Similarly, when the big columns of material desire increase, the clear water of consciousness is dried up
SB Canto 4
When one's mind and senses are attracted to sense objects for enjoyment, the mind becomes agitated. As a result of continually thinking of sense objects, one's real consciousness almost becomes lost, like the water in a lake that is gradually sucked up by the big grass straws on its bank.
In this verse it is very nicely explained how our original Kṛṣṇa consciousness becomes polluted and we gradually become almost completely forgetful of our relationship with the Supreme Lord. In the previous verse it is recommended that we should always keep in touch with the devotional service of the Lord so that the blazing fire of devotional service can gradually burn into ashes material desires and we can become liberated from the repetition of birth and death. This is also how we can indirectly keep our staunch faith in the lotus feet of the Supreme Personality of Godhead. When the mind is allowed to think of sense gratification continuously, it becomes the cause of our material bondage. If our mind is simply filled with sense gratification, even though we want Kṛṣṇa consciousness, by continuous practice we cannot forget the subject matter of sense gratification. If one takes up the sannyāsa order of life but is not able to control the mind, he will think of objects of sense gratification—namely family, society, expensive house, etc. Even though he goes to the Himalayas or the forest, his mind will continue thinking of the objects of sense gratification. In this way, gradually one's intelligence will be affected. When intelligence is affected, one loses his original taste for Kṛṣṇa consciousness.
The example given here is very appropriate. If a big lake is covered all around by long kuśa grass, just like columns, the waters dry up. Similarly, when the big columns of material desire increase, the clear water of consciousness is dried up. Therefore these columns of kuśa grass should be cut or thrown away from the very beginning. Śrī Caitanya Mahāprabhu has instructed that if from the very beginning we do not take care of unwanted grass in the paddy fields, the fertilizing agents or water will be used by them, and the paddy plants will dry up. The material desire for sense enjoyment is the cause of our falldown in this material world, and thus we suffer the threefold miseries and continuous birth, death, old age and disease. However, if we turn our desires toward the transcendental loving service of the Lord, our desires become purified. We cannot kill desires. We have to purify them of different designations. If we constantly think of being a member of a particular nation, society or family and continuously think about them, we become very strongly entangled in the conditioned life of birth and death. But if our desires are applied to the service of the Lord, they become purified, and thus we become immediately freed from material contamination.