find bigest island - backtracking, recursion

using System;

namespace islands
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // 0 - sea, 1 - unknown teritory
            int[,] sea = new int[,]
                {
                    { 1, 0, 1, 0, 0, 0, 1, },
                    { 0, 0, 1, 1, 1, 0, 1, },
                    { 1, 1, 1, 0, 0, 0, 1, },
                    { 0, 0, 1, 1, 0, 1, 1, },
                    { 0, 0, 0, 0, 0, 1, 1, },
                    { 1, 1, 0, 0, 1, 1, 1, },
                    { 0, 1, 0, 0, 0, 0, 0, },
                };

            //biggestIsland description
            int sizeBI = 0;
            int signBI = 0;

            //marking first island with number(2)
            int sign = 2;

            for (int row = 0; row < sea.GetLength(0); row++)
            {
                for (int column = 0; column < sea.GetLength(1); column++)
                {
                    if (sea[row, column] == 1)
                    {
                        int islandSize = 0;
                        MarkIsland(sea, row, column, sign, ref islandSize);

                        if (islandSize > sizeBI)
                        {
                            sizeBI = islandSize;
                            signBI = sign;
                        }

                        sign++;
                    }
                }
            }

            Console.WriteLine($"Biggest island is {signBI}, with size: {sizeBI}");
            OutputIsland(sea);
        }

        private static void MarkIsland(int[,] sea, int row, int column, int currentSign, ref int islandSize)
        {
            if (ValidField(sea, row, column) && FoundIsland(sea, row, column))
            {
                sea[row, column] = currentSign;
                islandSize++;

                MarkIsland(sea, row - 1, column, currentSign, ref islandSize);//up
                MarkIsland(sea, row + 1, column, currentSign, ref islandSize);//down
                MarkIsland(sea, row, column - 1, currentSign, ref islandSize);//left
                MarkIsland(sea, row, column + 1, currentSign, ref islandSize);//right
            }

        }

        private static bool FoundIsland(int[,] sea, int row, int column)
        {
            return sea[row, column] == 1;
        }

        private static bool ValidField(int[,] sea, int row, int column)
        {
            return row >= 0 && row < sea.GetLength(0) && column >= 0 && column < sea.GetLength(1);
        }

        private static void OutputIsland(int[,] sea)
        {
            for (int row = 0; row < sea.GetLength(0); row++)
            {
                for (int column = 0; column < sea.GetLength(1); column++)
                {
                    Console.Write($"{sea[row, column],7}");
                }
                Console.WriteLine();
            }
        }

    }
}