How can I randomly generate ASCII art land masses?

I am trying to randomly generate land masses, represented by ASCII art, using Python. I have the following code which either generates mostly water or mostly land. How could I achieve my end goal?

from random import *

water = "."
land = "#"

waterChance = 40
landChance = 100 - waterChance

width = 40
height = 20

prevTile = water

level = []

for i in range(height):
    level += [[]]
    for j in range(width):

        # change to ternary 
        if prevTile == water:
            waterChance += 10
        elif prevTile == land:
            waterChance -= 10

        if(waterChance == 50):
            waterChance += 5

        tile = randrange(1,101)

        if tile > waterChance:
            print(land, end='')
            prevTile = land
        elif tile <= waterChance:
            print(water, end='')
            prevTile = water
    print()