As found on inoutstar.com:
"A whale in your dream usually bears a positive significance, as the large water dwelling mammal represent your power and strength, your razor-sharp intuition, intelligence, your sense of spirituality and high level of awareness and perceptiveness. Besides these, the whale may also stand for your emotional and spiritual energy.
For instance, depending on the context in which you see the whale in your dream, you can interpret the emotional and psychological environment surrounding you everyday. If you see an aggressive whale in turbulent ocean waters, this means that the emotional and psychological environment in your everyday life is not the most appropriate one, as you may suffer from various emotional disorders or you may be overwhelmed by certain problems. On the other hand, if the whale in your dream is peacefully swimming in calm waters, then the emotional and psychological background totally fits you and you have reached a balance in your spiritual life.
The whale may also stand for great wealth and fortune, announcing opulence and plenitude to come in your life. But the large mammal may also stand for a business, a plan, an enterprise which is too big and important to handle, therefore you should consider looking for trustworthy associates if you want to get things done in an appropriate manner.
Seeing in your dream a whale approaching and pursuing a ship means that you will have to decide between two major tasks or undertakings. If the whale succeeds in attacking the ship, then you will deal with many problems in your waking life, but if the ship escapes the pursuit or the whale is killed by the sailors, then you will manage to solve all problems and conflicts and overcome all obstacles.
If we take into account language 'games', phrases or homonyms, the large mammal may stand for good times or grief, depending on the circumstances in which it is seen in the dream. If the whale is playful and happily swimming in the waters of the ocean, then it may be associated with the phrase 'having a whale of a time.' But if the whale is seen in a negative conjecture, then it may be interpreted as a pun for 'wail.'
Also, we should not forget about the fact that the water and especially the sea and ocean as dream symbols stand for our subconscious, all animals populating this medium are most of the times closely linked to our instincts and inner feelings and ideas we sometimes are not aware of. Consequently, the whale as a large water dwelling mammal is closely connected to our subconscious and it mirrors desires and thoughts we hide deep inside.
The whale is also associated with the massive fish appointed by God to swallow the prophet in the biblical myth of Jonah. The prophet remained 'buried' in the belly of the whale for 3 days and nights during which he repents and decides to come back to his religion and God who has thrown him inside the gigantic marine creature. After 3 days and 3 nights have gone, the whale spits Jonah out, but as a new man now, compared to the one who was swallowed. He re-embraced his religion and God again, therefore he is a new-born in a metaphorical sense, as his soul and mind are clear.
In conclusion, the whale is a symbol for renewal, re-birth and positive changes occurring in one's personality. At the same time, the massive water dwelling mammal is associated with shelter and protection and could be interpreted as maternal love and caring."
As for myself as a mermaid:
"A mermaid in your dream is a symbol of your current love or personal affairs, and its meaning depends on the action and the general atmosphere of the dream. If those elements were pleasant, you can expect things to go well, but if they were unpleasant or generated a feeling of confusion or dissatisfaction, the dream portends a disappointment."